System and method for on-demand unicast forwarding in a high performance computing environment

ABSTRACT

Systems and methods for on-demand unicast forwarding in a high performance computing environment, in accordance with an embodiment. An exemplary method can provide, at a computer comprising one or more microprocessors, a plurality of switches, a plurality of host channel adapters, and a plurality of hosts. The method can provide, at two rails, redundant connectivity between the plurality of hosts, wherein each rail comprises a set of the plurality of switches. The method can detect a disruption i connectivity between two hosts of the plurality of hosts. The method can re-establish communication between the two hosts of the plurality of hosts via unicast packets on an inter-rail link, the inter-rail link being provided between the two rails.

CLAIM OF PRIORITY AND CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claims the benefit ofpriority to, U.S. patent application entitled “SYSTEM AND METHOD FORUSING INFINIBAND ROUTING ALGORITHMS FOR ETHERNET FABRICS IN A HIGHPERFORMANCE COMPUTING ENVIRONMENT”, application Ser. No. 16/267,072,filed Feb. 4, 2019, which application claims the benefit of priority toU.S. Provisional Patent Application entitled “SYSTEM AND METHOD FORUSING INFINIBAND ROUTING ALGORITHMS FOR ETHERNET FABRICS IN A HIGHPERFORMANCE COMPUTING ENVIRONMENT”, Application No. 62/679,469, filed onJun. 1, 2018; each of which applications is incorporated by reference.

This application is also a continuation-in-part of U.S. patentapplication entitled “SYSTEM AND METHOD FOR REDUNDANT INDEPENDENTNETWORKS IN A HIGH PERFORMANCE COMPUTING ENVIRONMENT”, application Ser.No. 16/115,138, filed Aug. 28, 2018, which claims the benefit ofpriority to U.S. Provisional Patent Application entitled “SYSTEM ANDMETHOD FOR A RAIL NUMBER ASSOCIATION FOR CORRECT CONNECTIVITY IN A HIGHPERFORMANCE COMPUTING ENVIRONMENT”, Application No. 62/679,465, filed onJun. 1, 2018; and U.S. Provisional Patent Application entitled “SYSTEMAND METHOD FOR A REDUNDANT INDEPENDENT NETWORK IN A HIGH PERFORMANCECOMPUTING ENVIRONMENT”, Application No. 62/552,818, filed on Aug. 31,2017, each of which applications is incorporated by reference.

This application is also a continuation-in-part of U.S. PatentApplication entitled “SYSTEM AND METHOD FOR A MULTICAST SEND DUPLICATIONINSTEAD OF REPLICATION IN A HIGH PERFORMANCE COMPUTING ENVIRONMENT”,application Ser. No. 16/261,362, which application claims the benefit ofpriority to U.S. Provisional Patent Application entitled “SYSTEM ANDMETHOD FOR A MULTICAST SEND DUPLICATION INSTEAD OF REPLICATION IN A HIGHPERFORMANCE COMPUTING ENVIRONMENT”, Application No. 62/679,478, filed onJun. 1, 2018, each of which applications is incorporated by reference.

This application is related to U.S. Patent Application entitled “SYSTEMAND METHOD FOR SUPPORTING HETEROGENEOUS AND ASYMMETRIC DUAL RAIL FABRICCONFIGURATIONS IN A HIGH PERFORMANCE COMPUTING ENVIRONMENT”, filedconcurrently herewith (Attorney Docket No. ORACL-05860US3), and to U.S.Patent Application entitled “SYSTEM AND METHOD FOR A SINGLE LOGICAL IPSUBNET ACROSS MULTIPLE INDEPENDENT LAYER 2 (L2) SUBNETS IN A HIGHPERFORMANCE COMPUTING ENVIRONMENT”, filed concurrently herewith(Attorney Docket No. ORACL-05864US2), each of which applications isincorporated by reference.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND

As larger cloud computing architectures are introduced, the performanceand administrative bottlenecks associated with the traditional networkand storage have become a significant problem. There has been anincreased interest in using high performance interconnects such asInfiniBand (IB) and RoCE (RDMA over Converged Ethernet) technology asthe foundation for a cloud computing fabric. This is the general areathat embodiments of the invention are intended to address.

SUMMARY

Systems and methods for on-demand unicast forwarding in a highperformance computing environment, in accordance with an embodiment. Anexemplary method can provide, at a computer comprising one or moremicroprocessors, a plurality of switches, a plurality of host channeladapters, and a plurality of hosts. The method can provide, at tworails, redundant connectivity between the plurality of hosts, whereineach rail comprises a set of the plurality of switches. The method candetect a disruption i connectivity between two hosts of the plurality ofhosts. The method can re-establish communication between the two hostsof the plurality of hosts via unicast packets on an inter-rail link, theinter-rail link being provided between the two rails

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an illustration of an InfiniBand environment, in accordancewith an embodiment.

FIG. 2 shows an illustration of a partitioned cluster environment, inaccordance with an embodiment

FIG. 3 shows an illustration of a tree topology in a networkenvironment, in accordance with an embodiment.

FIG. 4 shows an exemplary shared port architecture, in accordance withan embodiment.

FIG. 5 shows an exemplary vSwitch architecture, in accordance with anembodiment.

FIG. 6 shows an exemplary vPort architecture, in accordance with anembodiment.

FIG. 7 shows an exemplary vSwitch architecture with prepopulated LIDs,in accordance with an embodiment.

FIG. 8 shows an exemplary vSwitch architecture with dynamic LIDassignment, in accordance with an embodiment.

FIG. 9 shows an exemplary vSwitch architecture with vSwitch with dynamicLID assignment and prepopulated LIDs, in accordance with an embodiment.

FIG. 10 shows an exemplary multi-subnet InfiniBand fabric, in accordancewith an embodiment.

FIG. 11 shows an interconnection between two subnets in a highperformance computing environment, in accordance with an embodiment.

FIG. 12 shows an interconnection between two subnets via a dual-portvirtual router configuration in a high performance computingenvironment, in accordance with an embodiment.

FIG. 13 shows a flowchart of a method for supporting dual-port virtualrouter in a high performance computing environment, in accordance withan embodiment.

FIG. 14 shows a system for supporting redundant independent networks ina high performance computing environment, in accordance with anembodiment.

FIG. 15 shows a system for supporting redundant independent networks ina high performance computing environment, in accordance with anembodiment.

FIG. 16 shows a system for supporting redundant independent networks ina high performance computing environment, in accordance with anembodiment.

FIG. 17 shows a system for supporting redundant independent networks ina high performance computing environment, in accordance with anembodiment.

FIG. 18 is a flowchart of a method for a redundant independent networkin a high performance computing environment

FIG. 19 shows a system for using InfiniBand (IB) routing algorithms forEthernet fabrics in a high performance computing environment, inaccordance with an embodiment.

FIG. 20 is a flowchart of a method for using InfiniBand routingalgorithms for Ethernet fabrics in a high performance computingenvironment.

FIG. 21 shows a system for on-demand unicast forwarding in a highperformance computing environment, in accordance with an embodiment.

FIG. 22 shows a system for on-demand unicast forwarding in a highperformance computing environment, in accordance with an embodiment.

FIG. 23 is a flowchart of a method for on-demand unicast forwarding in ahigh performance computing environment, in accordance with anembodiment.

DETAILED DESCRIPTION

The invention is illustrated, by way of example and not by way oflimitation, in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” or “some” embodiment(s) in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone. While specific implementations are discussed, it is understood thatthe specific implementations are provided for illustrative purposesonly. A person skilled in the relevant art will recognize that othercomponents and configurations may be used without departing from thescope and spirit of the invention.

Common reference numerals can be used to indicate like elementsthroughout the drawings and detailed description; therefore, referencenumerals used in a figure may or may not be referenced in the detaileddescription specific to such figure if the element is describedelsewhere.

In accordance with an embodiment, described herein are systems andmethods for on-demand unicast forwarding in a high performance computingenvironment in a high performance computing environment.

In some embodiments, the following description of the invention uses anInfiniBand™ (IB) network as an example for a high performance network.Throughout the following description, reference can be made to theInfiniBand™ specification (also referred to variously as the InfiniBandspecification, IB specification, or the legacy IB specification). Suchreference is understood to refer to the InfiniBand® Trade AssociationArchitecture Specification, Volume 1, Version 1.3, released March, 2015,available at http://www.inifinibandta.org, which is herein incorporatedby reference in its entirety. It will be apparent to those skilled inthe art that other types of high performance networks can be usedwithout limitation. The following description also uses the fat-treetopology as an example for a fabric topology. It will be apparent tothose skilled in the art that other types of fabric topologies can beused without limitation.

In some other embodiments, the following description uses a RoCE (RDMA(Remote Direct Memory Access) over Converged Ethernet). RDMA overConverged Ethernet (RoCE) is a standard protocol which enables RDMA'sefficient data transfer over Ethernet networks allowing transportoffload with hardware RDMA engine implementation, and superiorperformance. RoCE is a standard protocol defined in the InfiniBand TradeAssociation (IBTA) standard. RoCE makes use of UDP (user datagramprotocol) encapsulation allowing it to transcend Layer 3 networks. RDMAis a key capability natively used by the InfiniBand interconnecttechnology. Both InfiniBand and Ethernet RoCE share a common user APIbut have different physical and link layers.

In accordance with an embodiment, although portions of the specificationcontain reference to, in describing various implementations, anInfiniBand Fabric, one of ordinary skill in the art would readilyunderstand that the various embodiments described herein can also beimplemented in a RoCE Fabric.

To meet the demands of the cloud in the current era (e.g., Exascaleera), it is desirable for virtual machines to be able to utilize lowoverhead network communication paradigms such as Remote Direct MemoryAccess (RDMA). RDMA bypasses the OS stack and communicates directly withthe hardware, thus, pass-through technology like Single-Root I/OVirtualization (SR-IOV) network adapters can be used. In accordance withan embodiment, a virtual switch (vSwitch) SR-IOV architecture can beprovided for applicability in high performance lossless interconnectionnetworks. As network reconfiguration time is critical to makelive-migration a practical option, in addition to network architecture,a scalable and topology-agnostic dynamic reconfiguration mechanism canbe provided.

In accordance with an embodiment, and furthermore, routing strategiesfor virtualized environments using vSwitches can be provided, and anefficient routing algorithm for network topologies (e.g., Fat-Treetopologies) can be provided. The dynamic reconfiguration mechanism canbe further tuned to minimize imposed overhead in Fat-Trees.

In accordance with an embodiment of the invention, virtualization can bebeneficial to efficient resource utilization and elastic resourceallocation in cloud computing. Live migration makes it possible tooptimize resource usage by moving virtual machines (VMs) betweenphysical servers in an application transparent manner. Thus,virtualization can enable consolidation, on-demand provisioning ofresources, and elasticity through live migration.

InfiniBand™

InfiniBand™ (IB) is an open standard lossless network technologydeveloped by the InfiniBand™ Trade Association. The technology is basedon a serial point-to-point full-duplex interconnect that offers highthroughput and low latency communication, geared particularly towardshigh-performance computing (HPC) applications and datacenters.

The InfiniBand™ Architecture (IBA) supports a two-layer topologicaldivision. At the lower layer, IB networks are referred to as subnets,where a subnet can include a set of hosts interconnected using switchesand point-to-point links. At the higher level, an IB fabric constitutesone or more subnets, which can be interconnected using routers.

Within a subnet, hosts can be connected using switches andpoint-to-point links. Additionally, there can be a master managemententity, the subnet manager (SM), which resides on a designated device inthe subnet. The subnet manager is responsible for configuring,activating and maintaining the IB subnet. Additionally, the subnetmanager (SM) can be responsible for performing routing tablecalculations in an IB fabric. Here, for example, the routing of the IBnetwork aims at proper load balancing between all source and destinationpairs in the local subnet.

Through the subnet management interface, the subnet manager exchangescontrol packets, which are referred to as subnet management packets(SMPs), with subnet management agents (SMAs). The subnet managementagents reside on every IB subnet device. By using SMPs, the subnetmanager is able to discover the fabric, configure end nodes andswitches, and receive notifications from SMAs.

In accordance with an embodiment, intra-subnet routing in an IB networkcan be based on linear forwarding tables (LFTs) stored in the switches.The LFTs are calculated by the SM according to the routing mechanism inuse. In a subnet, Host Channel Adapter (HCA) ports on the end nodes andswitches are addressed using local identifiers (LIDs). Each entry in alinear forwarding table (LFT) consists of a destination LID (DLID) andan output port. Only one entry per LID in the table is supported. When apacket arrives at a switch, its output port is determined by looking upthe DLID in the forwarding table of the switch. The routing isdeterministic as packets take the same path in the network between agiven source-destination pair (LID pair).

Generally, all other subnet managers, excepting the master subnetmanager, act in standby mode for fault-tolerance. In a situation where amaster subnet manager fails, however, a new master subnet manager isnegotiated by the standby subnet managers. The master subnet manageralso performs periodic sweeps of the subnet to detect any topologychanges and reconfigure the network accordingly.

Furthermore, hosts and switches within a subnet can be addressed usinglocal identifiers (LIDs), and a single subnet can be limited to 49151unicast LIDs. Besides the LIDs, which are the local addresses that arevalid within a subnet, each IB device can have a 64-bit global uniqueidentifier (GUID). A GUID can be used to form a global identifier (GID),which is an IB layer three (L3) address.

The SM can calculate routing tables (i.e., the connections/routesbetween each pair of nodes within the subnet) at network initializationtime. Furthermore, the routing tables can be updated whenever thetopology changes, in order to ensure connectivity and optimalperformance. During normal operations, the SM can perform periodic lightsweeps of the network to check for topology changes. If a change isdiscovered during a light sweep or if a message (trap) signaling anetwork change is received by the SM, the SM can reconfigure the networkaccording to the discovered changes.

For example, the SM can reconfigure the network when the networktopology changes, such as when a link goes down, when a device is added,or when a link is removed. The reconfiguration steps can include thesteps performed during the network initialization. Furthermore, thereconfigurations can have a local scope that is limited to the subnets,in which the network changes occurred. Also, the segmenting of a largefabric with routers may limit the reconfiguration scope.

An example InfiniBand fabric is shown in FIG. 1, which shows anillustration of an InfiniBand environment 100, in accordance with anembodiment. In the example shown in FIG. 1, nodes A-E, 101-105, use theInfiniBand fabric, 120, to communicate, via the respective host channeladapters 111-115. In accordance with an embodiment, the various nodes,e.g., nodes A-E, 101-105, can be represented by various physicaldevices. In accordance with an embodiment, the various nodes, e.g.,nodes A-E, 101-105, can be represented by various virtual devices, suchas virtual machines.

Partitioning in InfiniBand

In accordance with an embodiment, IB networks can support partitioningas a security mechanism to provide for isolation of logical groups ofsystems sharing a network fabric. Each HCA port on a node in the fabriccan be a member of one or more partitions. Partition memberships aremanaged by a centralized partition manager, which can be part of the SM.The SM can configure partition membership information on each port as atable of 16-bit partition keys (P_Keys). The SM can also configureswitch and router ports with the partition enforcement tables containingP_Key information associated with the end-nodes that send or receivedata traffic through these ports. Additionally, in a general case,partition membership of a switch port can represent a union of allmembership indirectly associated with LIDs routed via the port in anegress (towards the link) direction.

In accordance with an embodiment, partitions are logical groups of portssuch that the members of a group can only communicate to other membersof the same logical group. At host channel adapters (HCAs) and switches,packets can be filtered using the partition membership information toenforce isolation. Packets with invalid partitioning information can bedropped as soon as the packets reaches an incoming port. In partitionedIB systems, partitions can be used to create tenant clusters. Withpartition enforcement in place, a node cannot communicate with othernodes that belong to a different tenant cluster. In this way, thesecurity of the system can be guaranteed even in the presence ofcompromised or malicious tenant nodes.

In accordance with an embodiment, for the communication between nodes,Queue Pairs (QPs) and End-to-End contexts (EECs) can be assigned to aparticular partition, except for the management Queue Pairs (QP0 andQP1). The P_Key information can then be added to every IB transportpacket sent. When a packet arrives at an HCA port or a switch, its P_Keyvalue can be validated against a table configured by the SM. If aninvalid P_Key value is found, the packet is discarded immediately. Inthis way, communication is allowed only between ports sharing apartition.

An example of IB partitions is shown in FIG. 2, which shows anillustration of a partitioned cluster environment, in accordance with anembodiment. In the example shown in FIG. 2, nodes A-E, 101-105, use theInfiniBand fabric, 120, to communicate, via the respective host channeladapters 111-115. The nodes A-E are arranged into partitions, namelypartition 1, 130, partition 2, 140, and partition 3, 150. Partition 1comprises node A 101 and node D 104. Partition 2 comprises node A 101,node B 102, and node C 103. Partition 3 comprises node C 103 and node E105. Because of the arrangement of the partitions, node D 104 and node E105 are not allowed to communicate as these nodes do not share apartition. Meanwhile, for example, node A 101 and node C 103 are allowedto communicate as these nodes are both members of partition 2, 140.

Virtual Machines in InfiniBand

During the last decade, the prospect of virtualized High PerformanceComputing (HPC) environments has improved considerably as CPU overheadhas been practically removed through hardware virtualization support;memory overhead has been significantly reduced by virtualizing theMemory Management Unit; storage overhead has been reduced by the use offast SAN storages or distributed networked file systems; and network I/Ooverhead has been reduced by the use of device passthrough techniqueslike Single Root Input/Output Virtualization (SR-IOV). It is nowpossible for clouds to accommodate virtual HPC (vHPC) clusters usinghigh performance interconnect solutions and deliver the necessaryperformance.

However, when coupled with lossless networks, such as InfiniBand (IB),certain cloud functionality, such as live migration of virtual machines(VMs), still remains an issue due to the complicated addressing androuting schemes used in these solutions. IB is an interconnectionnetwork technology offering high bandwidth and low latency, thus, isvery well suited for HPC and other communication intensive workloads.

The traditional approach for connecting IB devices to VMs is byutilizing SR-IOV with direct assignment. However, achieving livemigration of VMs assigned with IB Host Channel Adapters (HCAs) usingSR-IOV has proved to be challenging. Each IB connected node has threedifferent addresses: LID, GUID, and GID. When a live migration happens,one or more of these addresses change. Other nodes communicating withthe VM-in-migration can lose connectivity. When this happens, the lostconnection can be attempted to be renewed by locating the virtualmachine's new address to reconnect to by sending Subnet Administration(SA) path record queries to the IB Subnet Manager (SM).

IB uses three different types of addresses. A first type of address isthe 16 bits Local Identifier (LID). At least one unique LID is assignedto each HCA port and each switch by the SM. The LIDs are used to routetraffic within a subnet. Since the LID is 16 bits long, 65536 uniqueaddress combinations can be made, of which only 49151 (0x0001-0xBFFF)can be used as unicast addresses. Consequently, the number of availableunicast addresses defines the maximum size of an IB subnet. A secondtype of address is the 64 bits Global Unique Identifier (GUID) assignedby the manufacturer to each device (e.g. HCAs and switches) and each HCAport. The SM may assign additional subnet unique GUIDs to an HCA port,which is useful when SR-IOV is used. A third type of address is the 128bits Global Identifier (GID). The GID is a valid IPv6 unicast address,and at least one is assigned to each HCA port. The GID is formed bycombining a globally unique 64 bits prefix assigned by the fabricadministrator, and the GUID address of each HCA port.

Fat-Tree (FTree) Topologies and Routing

In accordance with an embodiment, some of the IB based HPC systemsemploy a fat-tree topology to take advantage of the useful propertiesfat-trees offer. These properties include full bisection-bandwidth andinherent fault-tolerance due to the availability of multiple pathsbetween each source destination pair. The initial idea behind fat-treeswas to employ fatter links between nodes, with more available bandwidth,as the tree moves towards the roots of the topology. The fatter linkscan help to avoid congestion in the upper-level switches and thebisection-bandwidth is maintained.

FIG. 3 shows an illustration of a tree topology in a networkenvironment, in accordance with an embodiment. As shown in FIG. 3, oneor more end nodes 201-204 can be connected in a network fabric 200. Thenetwork fabric 200 can be based on a fat-tree topology, which includes aplurality of leaf switches 211-214, and multiple spine switches or rootswitches 231-234. Additionally, the network fabric 200 can include oneor more intermediate switches, such as switches 221-224.

Also as shown in FIG. 3, each of the end nodes 201-204 can be amulti-homed node, i.e., a single node that is connected to two or moreparts of the network fabric 200 through multiple ports. For example, thenode 201 can include the ports H1 and H2, the node 202 can include theports H3 and H4, the node 203 can include the ports H5 and H6, and thenode 204 can include the ports H7 and H8.

Additionally, each switch can have multiple switch ports. For example,the root switch 231 can have the switch ports 1-2, the root switch 232can have the switch ports 3-4, the root switch 233 can have the switchports 5-6, and the root switch 234 can have the switch ports 7-8.

In accordance with an embodiment, the fat-tree routing mechanism is oneof the most popular routing algorithm for IB based fat-tree topologies.The fat-tree routing mechanism is also implemented in the OFED (OpenFabric Enterprise Distribution—a standard software stack for buildingand deploying IB based applications) subnet manager, OpenSM.

The fat-tree routing mechanism aims to generate LFTs that evenly spreadshortest-path routes across the links in the network fabric. Themechanism traverses the fabric in the indexing order and assigns targetLIDs of the end nodes, and thus the corresponding routes, to each switchport. For the end nodes connected to the same leaf switch, the indexingorder can depend on the switch port to which the end node is connected(i.e., port numbering sequence). For each port, the mechanism canmaintain a port usage counter, and can use this port usage counter toselect a least-used port each time a new route is added.

In accordance with an embodiment, in a partitioned subnet, nodes thatare not members of a common partition are not allowed to communicate.Practically, this means that some of the routes assigned by the fat-treerouting algorithm are not used for the user traffic. The problem ariseswhen the fat tree routing mechanism generates LFTs for those routes thesame way it does for the other functional paths. This behavior canresult in degraded balancing on the links, as nodes are routed in theorder of indexing. As routing can be performed oblivious to thepartitions, fat-tree routed subnets, in general, provide poor isolationamong partitions.

In accordance with an embodiment, a Fat-Tree is a hierarchical networktopology that can scale with the available network resources. Moreover,Fat-Trees are easy to build using commodity switches placed on differentlevels of the hierarchy. Different variations of Fat-Trees are commonlyavailable, including k-ary-n-trees, Extended Generalized Fat-Trees(XGFTs), Parallel Ports Generalized Fat-Trees (PGFTs) and Real LifeFat-Trees (RLFTs).

A k-ary-n-tree is an n level Fat-Tree with k^(n) end nodes and n·k^(n-1)switches, each with 2 k ports. Each switch has an equal number of up anddown connections in the tree. XGFT Fat-Tree extends k-ary-n-trees byallowing both different number of up and down connections for theswitches, and different number of connections at each level in the tree.The PGFT definition further broadens the XGFT topologies and permitsmultiple connections between switches. A large variety of topologies canbe defined using XGFTs and PGFTs. However, for practical purposes, RLFT,which is a restricted version of PGFT, is introduced to define Fat-Treescommonly found in today's HPC clusters. An RLFT uses the same port-countswitches at all levels in the Fat-Tree.

Input/Output (I/O) Virtualization

In accordance with an embodiment, I/O Virtualization (IOV) can provideavailability of I/O by allowing virtual machines (VMs) to access theunderlying physical resources. The combination of storage traffic andinter-server communication impose an increased load that may overwhelmthe I/O resources of a single server, leading to backlogs and idleprocessors as they are waiting for data. With the increase in number ofI/O requests, IOV can provide availability; and can improve performance,scalability and flexibility of the (virtualized) I/O resources to matchthe level of performance seen in modern CPU virtualization.

In accordance with an embodiment, IOV is desired as it can allow sharingof I/O resources and provide protected access to the resources from theVMs. IOV decouples a logical device, which is exposed to a VM, from itsphysical implementation. Currently, there can be different types of IOVtechnologies, such as emulation, paravirtualization, direct assignment(DA), and single root-I/O virtualization (SR-IOV).

In accordance with an embodiment, one type of IOV technology is softwareemulation. Software emulation can allow for a decoupledfront-end/back-end software architecture. The front-end can be a devicedriver placed in the VM, communicating with the back-end implemented bya hypervisor to provide I/O access. The physical device sharing ratio ishigh and live migrations of VMs are possible with just a fewmilliseconds of network downtime. However, software emulation introducesadditional, undesired computational overhead.

In accordance with an embodiment, another type of IOV technology isdirect device assignment. Direct device assignment involves a couplingof I/O devices to VMs, with no device sharing between VMs. Directassignment or device passthrough, provides near to native performancewith minimum overhead. The physical device bypasses the hypervisor andis directly attached to the VM. However, a downside of such directdevice assignment is limited scalability, as there is no sharing amongvirtual machines—one physical network card is coupled with one VM.

In accordance with an embodiment, Single Root IOV (SR-IOV) can allow aphysical device to appear through hardware virtualization as multipleindependent lightweight instances of the same device. These instancescan be assigned to VMs as passthrough devices, and accessed as VirtualFunctions (VFs). The hypervisor accesses the device through a unique(per device), fully featured Physical Function (PF). SR-IOV eases thescalability issue of pure direct assignment. However, a problempresented by SR-IOV is that it can impair VM migration. Among these IOVtechnologies, SR-IOV can extend the PCI Express (PCIe) specificationwith the means to allow direct access to a single physical device frommultiple VMs while maintaining near to native performance. Thus, SR-IOVcan provide good performance and scalability.

SR-IOV allows a PCIe device to expose multiple virtual devices that canbe shared between multiple guests by allocating one virtual device toeach guest. Each SR-IOV device has at least one physical function (PF)and one or more associated virtual functions (VF). A PF is a normal PCIefunction controlled by the virtual machine monitor (VMM), or hypervisor,whereas a VF is a light-weight PCIe function. Each VF has its own baseaddress (BAR) and is assigned with a unique requester ID that enablesI/O memory management unit (IOMMU) to differentiate between the trafficstreams to/from different VFs. The IOMMU also apply memory and interrupttranslations between the PF and the VFs.

Unfortunately, however, direct device assignment techniques pose abarrier for cloud providers in situations where transparent livemigration of virtual machines is desired for data center optimization.The essence of live migration is that the memory contents of a VM arecopied to a remote hypervisor. Then the VM is paused at the sourcehypervisor, and the VM's operation is resumed at the destination. Whenusing software emulation methods, the network interfaces are virtual sotheir internal states are stored into the memory and get copied as well.Thus the downtime could be brought down to a few milliseconds.

However, migration becomes more difficult when direct device assignmenttechniques, such as SR-IOV, are used. In such situations, a completeinternal state of the network interface cannot be copied as it is tiedto the hardware. The SR-IOV VFs assigned to a VM are instead detached,the live migration will run, and a new VF will be attached at thedestination. In the case of InfiniBand and SR-IOV, this process canintroduce downtime in the order of seconds. Moreover, in an SR-IOVshared port model the addresses of the VM will change after themigration, causing additional overhead in the SM and a negative impacton the performance of the underlying network fabric.

InfiniBand SR-IOV Architecture—Shared Port

There can be different types of SR-IOV models, e.g. a shared port model,a virtual switch model, and a virtual port model.

FIG. 4 shows an exemplary shared port architecture, in accordance withan embodiment. As depicted in the figure, a host 300 (e.g., a hostchannel adapter) can interact with a hypervisor 310, which can assignthe various virtual functions 330, 340, 350, to a number of virtualmachines. As well, the physical function can be handled by thehypervisor 310.

In accordance with an embodiment, when using a shared port architecture,such as that depicted in FIG. 4, the host, e.g., HCA, appears as asingle port in the network with a single shared LID and shared QueuePair (QP) space between the physical function 320 and the virtualfunctions 330, 350, 350. However, each function (i.e., physical functionand virtual functions) can have their own GID.

As shown in FIG. 4, in accordance with an embodiment, different GIDs canbe assigned to the virtual functions and the physical function, and thespecial queue pairs, QP0 and QP1 (i.e., special purpose queue pairs thatare used for InfiniBand management packets), are owned by the physicalfunction. These QPs are exposed to the VFs as well, but the VFs are notallowed to use QP0 (all SMPs coming from VFs towards QP0 are discarded),and QP1 can act as a proxy of the actual QP1 owned by the PF.

In accordance with an embodiment, the shared port architecture can allowfor highly scalable data centers that are not limited by the number ofVMs (which attach to the network by being assigned to the virtualfunctions), as the LID space is only consumed by physical machines andswitches in the network.

However, a shortcoming of the shared port architecture is the inabilityto provide transparent live migration, hindering the potential forflexible VM placement. As each LID is associated with a specifichypervisor, and shared among all VMs residing on the hypervisor, amigrating VM (i.e., a virtual machine migrating to a destinationhypervisor) has to have its LID changed to the LID of the destinationhypervisor. Furthermore, as a consequence of the restricted QP0 access,a subnet manager cannot run inside a VM.

InfiniBand SR-IOV Architecture Models—Virtual Switch (vSwitch)

FIG. 5 shows an exemplary vSwitch architecture, in accordance with anembodiment. As depicted in the figure, a host 400 (e.g., a host channeladapter) can interact with a hypervisor 410, which can assign thevarious virtual functions 430, 440, 450, to a number of virtualmachines. As well, the physical function can be handled by thehypervisor 410. A virtual switch 415 can also be handled by thehypervisor 401.

In accordance with an embodiment, in a vSwitch architecture each virtualfunction 430, 440, 450 is a complete virtual Host Channel Adapter(vHCA), meaning that the VM assigned to a VF is assigned a complete setof IB addresses (e.g., GID, GUID, LID) and a dedicated QP space in thehardware. For the rest of the network and the SM, the HCA 400 looks likea switch, via the virtual switch 415, with additional nodes connected toit. The hypervisor 410 can use the PF 420, and the VMs (attached to thevirtual functions) use the VFs.

In accordance with an embodiment, a vSwitch architecture providetransparent virtualization. However, because each virtual function isassigned a unique LID, the number of available LIDs gets consumedrapidly. As well, with many LID addresses in use (i.e., one each foreach physical function and each virtual function), more communicationpaths have to be computed by the SM and more Subnet Management Packets(SMPs) have to be sent to the switches in order to update their LFTs.For example, the computation of the communication paths might takeseveral minutes in large networks. Because LID space is limited to 49151unicast LIDs, and as each VM (via a VF), physical node, and switchoccupies one LID each, the number of physical nodes and switches in thenetwork limits the number of active VMs, and vice versa.

InfiniBand SR-IOV Architecture Models—Virtual Port (vPort)

FIG. 6 shows an exemplary vPort concept, in accordance with anembodiment. As depicted in the figure, a host 300 (e.g., a host channeladapter) can interact with a hypervisor 410, which can assign thevarious virtual functions 330, 340, 350, to a number of virtualmachines. As well, the physical function can be handled by thehypervisor 310.

In accordance with an embodiment, the vPort concept is loosely definedin order to give freedom of implementation to vendors (e.g. thedefinition does not rule that the implementation has to be SRIOVspecific), and a goal of the vPort is to standardize the way VMs arehandled in subnets. With the vPort concept, both SR-IOV Shared-Port-likeand vSwitch-like architectures or a combination of both, that can bemore scalable in both the space and performance domains, can be defined.A vPort supports optional LIDs, and unlike the Shared-Port, the SM isaware of all the vPorts available in a subnet even if a vPort is notusing a dedicated LID.

InfiniBand SR-IOV Architecture Models—vSwitch with Prepopulated LIDs

In accordance with an embodiment, the present disclosure provides asystem and method for providing a vSwitch architecture with prepopulatedLIDs.

FIG. 7 shows an exemplary vSwitch architecture with prepopulated LIDs,in accordance with an embodiment. As depicted in the figure, a number ofswitches 501-504 can provide communication within the network switchedenvironment 600 (e.g., an IB subnet) between members of a fabric, suchas an InfiniBand fabric. The fabric can include a number of hardwaredevices, such as host channel adapters 510, 520, 530. Each of the hostchannel adapters 510, 520, 530, can in turn interact with a hypervisor511, 521, and 531, respectively. Each hypervisor can, in turn, inconjunction with the host channel adapter it interacts with, setup andassign a number of virtual functions 514, 515, 516, 524, 525, 526, 534,535, 536, to a number of virtual machines. For example, virtual machine1 550 can be assigned by the hypervisor 511 to virtual function 1 514.Hypervisor 511 can additionally assign virtual machine 2 551 to virtualfunction 2 515, and virtual machine 3 552 to virtual function 3 516.Hypervisor 531 can, in turn, assign virtual machine 4 553 to virtualfunction 1 534. The hypervisors can access the host channel adaptersthrough a fully featured physical function 513, 523, 533, on each of thehost channel adapters.

In accordance with an embodiment, each of the switches 501-504 cancomprise a number of ports (not shown), which are used in setting alinear forwarding table in order to direct traffic within the networkswitched environment 600.

In accordance with an embodiment, the virtual switches 512, 522, and532, can be handled by their respective hypervisors 511, 521, 531. Insuch a vSwitch architecture each virtual function is a complete virtualHost Channel Adapter (vHCA), meaning that the VM assigned to a VF isassigned a complete set of IB addresses (e.g., GID, GUID, LID) and adedicated QP space in the hardware. For the rest of the network and theSM (not shown), the HCAs 510, 520, and 530 look like a switch, via thevirtual switches, with additional nodes connected to them.

In accordance with an embodiment, the present disclosure provides asystem and method for providing a vSwitch architecture with prepopulatedLIDs. Referring to FIG. 7, the LIDs are prepopulated to the variousphysical functions 513, 523, 533, as well as the virtual functions514-516, 524-526, 534-536 (even those virtual functions not currentlyassociated with an active virtual machine). For example, physicalfunction 513 is prepopulated with LID 1, while virtual function 1 534 isprepopulated with LID 10. The LIDs are prepopulated in an SR-IOVvSwitch-enabled subnet when the network is booted. Even when not all ofthe VFs are occupied by VMs in the network, the populated VFs areassigned with a LID as shown in FIG. 7.

In accordance with an embodiment, much like physical host channeladapters can have more than one port (two ports are common forredundancy), virtual HCAs can also be represented with two ports and beconnected via one, two or more virtual switches to the external IBsubnet.

In accordance with an embodiment, in a vSwitch architecture withprepopulated LIDs, each hypervisor can consume one LID for itselfthrough the PF and one more LID for each additional VF. The sum of allthe VFs available in all hypervisors in an IB subnet, gives the maximumamount of VMs that are allowed to run in the subnet. For example, in anIB subnet with 16 virtual functions per hypervisor in the subnet, theneach hypervisor consumes 17 LIDs (one LID for each of the 16 virtualfunctions plus one LID for the physical function) in the subnet. In suchan IB subnet, the theoretical hypervisor limit for a single subnet isruled by the number of available unicast LIDs and is: 2891 (49151available LIDs divided by 17 LIDs per hypervisor), and the total numberof VMs (i.e., the limit) is 46256 (2891 hypervisors times 16 VFs perhypervisor). (In actuality, these numbers are actually smaller sinceeach switch, router, or dedicated SM node in the IB subnet consumes aLID as well). Note that the vSwitch does not need to occupy anadditional LID as it can share the LID with the PF

In accordance with an embodiment, in a vSwitch architecture withprepopulated LIDs, communication paths are computed for all the LIDs thefirst time the network is booted. When a new VM needs to be started thesystem does not have to add a new LID in the subnet, an action thatwould otherwise cause a complete reconfiguration of the network,including path recalculation, which is the most time consuming part.Instead, an available port for a VM is located (i.e., an availablevirtual function) in one of the hypervisors and the virtual machine isattached to the available virtual function.

In accordance with an embodiment, a vSwitch architecture withprepopulated LIDs also allows for the ability to calculate and usedifferent paths to reach different VMs hosted by the same hypervisor.Essentially, this allows for such subnets and networks to use a LID MaskControl (LMC) like feature to provide alternative paths towards onephysical machine, without being bound by the limitation of the LMC thatrequires the LIDs to be sequential. The freedom to use non-sequentialLIDs is particularly useful when a VM needs to be migrated and carry itsassociated LID to the destination.

In accordance with an embodiment, along with the benefits shown above ofa vSwitch architecture with prepopulated LIDs, certain considerationscan be taken into account. For example, because the LIDs areprepopulated in an SR-IOV vSwitch-enabled subnet when the network isbooted, the initial path computation (e.g., on boot-up) can take longerthan if the LIDs were not pre-populated.

InfiniBand SR-IOV Architecture Models—vSwitch with Dynamic LIDAssignment

In accordance with an embodiment, the present disclosure provides asystem and method for providing a vSwitch architecture with dynamic LIDassignment.

FIG. 8 shows an exemplary vSwitch architecture with dynamic LIDassignment, in accordance with an embodiment. As depicted in the figure,a number of switches 501-504 can provide communication within thenetwork switched environment 700 (e.g., an IB subnet) between members ofa fabric, such as an InfiniBand fabric. The fabric can include a numberof hardware devices, such as host channel adapters 510, 520, 530. Eachof the host channel adapters 510, 520, 530, can in turn interact with ahypervisor 511, 521, 531, respectively. Each hypervisor can, in turn, inconjunction with the host channel adapter it interacts with, setup andassign a number of virtual functions 514, 515, 516, 524, 525, 526, 534,535, 536, to a number of virtual machines. For example, virtual machine1 550 can be assigned by the hypervisor 511 to virtual function 1 514.Hypervisor 511 can additionally assign virtual machine 2 551 to virtualfunction 2 515, and virtual machine 3 552 to virtual function 3 516.Hypervisor 531 can, in turn, assign virtual machine 4 553 to virtualfunction 1 534. The hypervisors can access the host channel adaptersthrough a fully featured physical function 513, 523, 533, on each of thehost channel adapters.

In accordance with an embodiment, each of the switches 501-504 cancomprise a number of ports (not shown), which are used in setting alinear forwarding table in order to direct traffic within the networkswitched environment 700.

In accordance with an embodiment, the virtual switches 512, 522, and532, can be handled by their respective hypervisors 511, 521, 531. Insuch a vSwitch architecture each virtual function is a complete virtualHost Channel Adapter (vHCA), meaning that the VM assigned to a VF isassigned a complete set of IB addresses (e.g., GID, GUID, LID) and adedicated QP space in the hardware. For the rest of the network and theSM (not shown), the HCAs 510, 520, and 530 look like a switch, via thevirtual switches, with additional nodes connected to them.

In accordance with an embodiment, the present disclosure provides asystem and method for providing a vSwitch architecture with dynamic LIDassignment. Referring to FIG. 8, the LIDs are dynamically assigned tothe various physical functions 513, 523, 533, with physical function 513receiving LID 1, physical function 523 receiving LID 2, and physicalfunction 533 receiving LID 3. Those virtual functions that areassociated with an active virtual machine can also receive a dynamicallyassigned LID. For example, because virtual machine 1 550 is active andassociated with virtual function 1 514, virtual function 514 can beassigned LID 5. Likewise, virtual function 2 515, virtual function 3516, and virtual function 1 534 are each associated with an activevirtual function. Because of this, these virtual functions are assignedLIDs, with LID 7 being assigned to virtual function 2 515, LID 11 beingassigned to virtual function 3 516, and LID 9 being assigned to virtualfunction 1 534. Unlike vSwitch with prepopulated LIDs, those virtualfunctions not currently associated with an active virtual machine do notreceive a LID assignment.

In accordance with an embodiment, with the dynamic LID assignment, theinitial path computation can be substantially reduced. When the networkis booting for the first time and no VMs are present then a relativelysmall number of LIDs can be used for the initial path calculation andLFT distribution.

In accordance with an embodiment, much like physical host channeladapters can have more than one port (two ports are common forredundancy), virtual HCAs can also be represented with two ports and beconnected via one, two or more virtual switches to the external IBsubnet.

In accordance with an embodiment, when a new VM is created in a systemutilizing vSwitch with dynamic LID assignment, a free VM slot is foundin order to decide on which hypervisor to boot the newly added VM, and aunique non-used unicast LID is found as well. However, there are noknown paths in the network and the LFTs of the switches for handling thenewly added LID. Computing a new set of paths in order to handle thenewly added VM is not desirable in a dynamic environment where severalVMs may be booted every minute. In large IB subnets, computing a new setof routes can take several minutes, and this procedure would have torepeat each time a new VM is booted.

Advantageously, in accordance with an embodiment, because all the VFs ina hypervisor share the same uplink with the PF, there is no need tocompute a new set of routes. It is only needed to iterate through theLFTs of all the physical switches in the network, copy the forwardingport from the LID entry that belongs to the PF of the hypervisor—wherethe VM is created—to the newly added LID, and send a single SMP toupdate the corresponding LFT block of the particular switch. Thus thesystem and method avoids the need to compute a new set of routes.

In accordance with an embodiment, the LIDs assigned in the vSwitch withdynamic LID assignment architecture do not have to be sequential. Whencomparing the LIDs assigned on VMs on each hypervisor in vSwitch withprepopulated LIDs versus vSwitch with dynamic LID assignment, it isnotable that the LIDs assigned in the dynamic LID assignmentarchitecture are non-sequential, while those prepopulated in aresequential in nature. In the vSwitch dynamic LID assignmentarchitecture, when a new VM is created, the next available LID is usedthroughout the lifetime of the VM. Conversely, in a vSwitch withprepopulated LIDs, each VM inherits the LID that is already assigned tothe corresponding VF, and in a network without live migrations, VMsconsecutively attached to a given VF get the same LID.

In accordance with an embodiment, the vSwitch with dynamic LIDassignment architecture can resolve the drawbacks of the vSwitch withprepopulated LIDs architecture model at a cost of some additionalnetwork and runtime SM overhead. Each time a VM is created, the LFTs ofthe physical switches in the subnet are updated with the newly added LIDassociated with the created VM. One subnet management packet (SMP) perswitch is needed to be sent for this operation. The LMC-likefunctionality is also not available, because each VM is using the samepath as its host hypervisor. However, there is no limitation on thetotal amount of VFs present in all hypervisors, and the number of VFsmay exceed that of the unicast LID limit. Of course, not all of the VFsare allowed to be attached on active VMs simultaneously if this is thecase, but having more spare hypervisors and VFs adds flexibility fordisaster recovery and optimization of fragmented networks when operatingclose to the unicast LID limit.

InfiniBand SR-IOV Architecture Models—vSwitch with Dynamic LIDAssignment and Prepopulated LIDs

FIG. 9 shows an exemplary vSwitch architecture with vSwitch with dynamicLID assignment and prepopulated LIDs, in accordance with an embodiment.As depicted in the figure, a number of switches 501-504 can providecommunication within the network switched environment 800 (e.g., an IBsubnet) between members of a fabric, such as an InfiniBand fabric. Thefabric can include a number of hardware devices, such as host channeladapters 510, 520, 530. Each of the host channel adapters 510, 520, 530,can in turn interact with a hypervisor 511, 521, and 531, respectively.Each hypervisor can, in turn, in conjunction with the host channeladapter it interacts with, setup and assign a number of virtualfunctions 514, 515, 516, 524, 525, 526, 534, 535, 536, to a number ofvirtual machines. For example, virtual machine 1 550 can be assigned bythe hypervisor 511 to virtual function 1 514. Hypervisor 511 canadditionally assign virtual machine 2 551 to virtual function 2 515.Hypervisor 521 can assign virtual machine 3 552 to virtual function 3526. Hypervisor 531 can, in turn, assign virtual machine 4 553 tovirtual function 2 535. The hypervisors can access the host channeladapters through a fully featured physical function 513, 523, 533, oneach of the host channel adapters.

In accordance with an embodiment, each of the switches 501-504 cancomprise a number of ports (not shown), which are used in setting alinear forwarding table in order to direct traffic within the networkswitched environment 800.

In accordance with an embodiment, the virtual switches 512, 522, and532, can be handled by their respective hypervisors 511, 521, 531. Insuch a vSwitch architecture each virtual function is a complete virtualHost Channel Adapter (vHCA), meaning that the VM assigned to a VF isassigned a complete set of IB addresses (e.g., GID, GUID, LID) and adedicated QP space in the hardware. For the rest of the network and theSM (not shown), the HCAs 510, 520, and 530 look like a switch, via thevirtual switches, with additional nodes connected to them.

In accordance with an embodiment, the present disclosure provides asystem and method for providing a hybrid vSwitch architecture withdynamic LID assignment and prepopulated LIDs. Referring to FIG. 9,hypervisor 511 can be arranged with vSwitch with prepopulated LIDsarchitecture, while hypervisor 521 can be arranged with vSwitch withprepopulated LIDs and dynamic LID assignment. Hypervisor 531 can bearranged with vSwitch with dynamic LID assignment. Thus, the physicalfunction 513 and virtual functions 514-516 have their LIDs prepopulated(i.e., even those virtual functions not attached to an active virtualmachine are assigned a LID). Physical function 523 and virtual function1 524 can have their LIDs prepopulated, while virtual function 2 and 3,525 and 526, have their LIDs dynamically assigned (i.e., virtualfunction 2 525 is available for dynamic LID assignment, and virtualfunction 3 526 has a LID of 11 dynamically assigned as virtual machine 3552 is attached). Finally, the functions (physical function and virtualfunctions) associated with hypervisor 3 531 can have their LIDsdynamically assigned. This results in virtual functions 1 and 3, 534 and536, are available for dynamic LID assignment, while virtual function 2535 has LID of 9 dynamically assigned as virtual machine 4 553 isattached there.

In accordance with an embodiment, such as that depicted in FIG. 9, whereboth vSwitch with prepopulated LIDs and vSwitch with dynamic LIDassignment are utilized (independently or in combination within anygiven hypervisor), the number of prepopulated LIDs per host channeladapter can be defined by a fabric administrator and can be in the rangeof 0<=prepopulated VFs<=Total VFs (per host channel adapter), and theVFs available for dynamic LID assignment can be found by subtracting thenumber of prepopulated VFs from the total number of VFs (per hostchannel adapter).

In accordance with an embodiment, much like physical host channeladapters can have more than one port (two ports are common forredundancy), virtual HCAs can also be represented with two ports and beconnected via one, two or more virtual switches to the external IBsubnet.

InfiniBand—Inter-Subnet Communication (Fabric Manager)

In accordance with an embodiment, in addition to providing an InfiniBandfabric within a single subnet, embodiments of the current disclosure canalso provide for an InfiniBand fabric that spans two or more subnets.

FIG. 10 shows an exemplary multi-subnet InfiniBand fabric, in accordancewith an embodiment. As depicted in the figure, within subnet A 1000, anumber of switches 1001-1004 can provide communication within subnet A1000 (e.g., an IB subnet) between members of a fabric, such as anInfiniBand fabric. The fabric can include a number of hardware devices,such as, for example, channel adapter 1010. Host channel adapter 1010can in turn interact with a hypervisor 1011. The hypervisor can, inturn, in conjunction with the host channel adapter it interacts with,setup a number of virtual functions 1014. The hypervisor canadditionally assign virtual machines to each of the virtual functions,such as virtual machine 1 1015 being assigned to virtual function 11014. The hypervisor can access their associated host channel adaptersthrough a fully featured physical function, such as physical function1013, on each of the host channel adapters. Within subnet B 1040, anumber of switches 1021-1024 can provide communication within subnet B1040 (e.g., an IB subnet) between members of a fabric, such as anInfiniBand fabric. The fabric can include a number of hardware devices,such as, for example, channel adapter 1030. Host channel adapter 1030can in turn interact with a hypervisor 1031. The hypervisor can, inturn, in conjunction with the host channel adapter it interacts with,setup a number of virtual functions 1034. The hypervisor canadditionally assign virtual machines to each of the virtual functions,such as virtual machine 2 1035 being assigned to virtual function 21034. The hypervisor can access their associated host channel adaptersthrough a fully featured physical function, such as physical function1033, on each of the host channel adapters. It is noted that althoughonly one host channel adapter is shown within each subnet (i.e., subnetA and subnet B), it is to be understood that a plurality of host channeladapters, and their corresponding components, can be included withineach subnet.

In accordance with an embodiment, each of the host channel adapters canadditionally be associated with a virtual switch, such as virtual switch1012 and virtual switch 1032, and each HCA can be set up with adifferent architecture model, as discussed above. Although both subnetswithin FIG. 10 are shown as using a vSwitch with prepopulated LIDarchitecture model, this is not meant to imply that all such subnetconfigurations can follow a similar architecture model.

In accordance with an embodiment, at least one switch within each subnetcan be associated with a router, such as switch 1002 within subnet A1000 being associated with router 1005, and switch 1021 within subnet B1040 being associated with router 1006.

In accordance with an embodiment, at least one device (e.g., a switch, anode . . . etc.) can be associated with a fabric manager (not shown).The fabric manager can be used, for example, to discover inter-subnetfabric topology, create a fabric profile (e.g., a virtual machine fabricprofile), build virtual machine related database objects that forms thebasis for building a virtual machine fabric profile. In addition, thefabric manager can define legal inter-subnet connectivity in terms ofwhich subnets are allowed to communicate via which router ports usingwhich partition numbers.

In accordance with an embodiment, when traffic at an originating source,such as virtual machine 1 within subnet A, is addressed to a destinationin a different subnet, such as virtual machine 2 within subnet B, thetraffic can be addressed to the router within subnet A, i.e., router1005, which can then pass the traffic to subnet B via its link withrouter 1006.

Virtual Dual Port Router

In accordance with an embodiment, a dual port router abstraction canprovide a simple way for enabling subnet-to-subnet router functionalityto be defined based on a switch hardware implementation that has theability to do GRH (global route header) to LRH (local route header)conversion in addition to performing normal LRH based switching.

In accordance with an embodiment, a virtual dual-port router canlogically be connected outside a corresponding switch port. This virtualdual-port router can provide an InfiniBand specification compliant viewto a standard management entity, such as a Subnet Manager.

In accordance with an embodiment, a dual-ported router model impliesthat different subnets can be connected in a way where each subnet fullycontrols the forwarding of packets as well as address mappings in theingress path to the subnet, and without impacting the routing andlogical connectivity within either of the incorrectly connected subnets.

In accordance with an embodiment, in a situation involving anincorrectly connected fabric, the use of a virtual dual-port routerabstraction can also allow a management entity, such as a Subnet Managerand IB diagnostic software, to behave correctly in the presence ofun-intended physical connectivity to a remote subnet.

FIG. 11 shows an interconnection between two subnets in a highperformance computing environment, in accordance with an embodiment.Prior to configuration with a virtual dual port router, a switch 1120 insubnetA 1101 can be connected through a switch port 1121 of switch 1120,via a physical connection 1110, to a switch 1130 in subnet B 1102, via aswitch port 1131 of switch 1130. In such an embodiment, each switchport, 1121 and 1131, can act both as switch ports and router ports.

In accordance with an embodiment, a problem with this configuration isthat a management entity, such as a subnet manager in an InfiniBandsubnet, cannot distinguish between a physical port that is both a switchport and a router port. In such a situation, a SM can treat the switchport as having a router port connected to that switch port. But if theswitch port is connected to another subnet, via, for example, a physicallink, with another subnet manager, then the subnet manager can be ableto send a discovery message out on the physical link. However, such adiscovery message cannot be allowed at the other subnet.

FIG. 12 shows an interconnection between two subnets via a dual-portvirtual router configuration in a high performance computingenvironment, in accordance with an embodiment.

In accordance with an embodiment, after configuration, a dual-portvirtual router configuration can be provided such that a subnet managersees a proper end node, signifying an end of the subnet that the subnetmanager is responsible for.

In accordance with an embodiment, at a switch 1220 in subnetA 1201, aswitch port can be connected (i.e., logically connected) to a routerport 1211 in a virtual router 1210 via a virtual link 1223. The virtualrouter 1210 (e.g., a dual-port virtual router), which while shown asbeing external to the switch 1220 can, in embodiments, be logicallycontained within the switch 1220, can also comprise a second routerport, router port II 1212. In accordance with an embodiment, a physicallink 1203, which can have two ends, can connect the subnetA 1201 viafirst end of the physical link with subnet B 1202 via a second end ofthe physical link, via router port II 1212 and router port II 1232,contained in virtual router 1230 in subnet B 1202. Virtual router 1230can additionally comprise router port 1231, which can be connected(i.e., logically connected) to switch port 1241 on switch 1240 via avirtual link 1233.

In accordance with an embodiment, a subnet manager (not shown) onsubnetA can detect router port 1211, on virtual router 1210 as an endpoint of the subnet that the subnet manager controls. The dual-portvirtual router abstraction can allow the subnet manager on subnet A todeal with subnetA in a usual manner (e.g., as defined per the InfiniBandspecification). At the subnet management agent level, the dual-portvirtual router abstraction can be provided such that the SM sees thenormal switch port, and then at the SMA level, the abstraction thatthere is another port connected to the switch port, and this port is arouter port on a dual-port virtual router. In the local SM, aconventional fabric topology can continue to be used (the SM sees theport as a standard switch port in the topology), and thus the SM seesthe router port as an end port. Physical connection can be made betweentwo switch ports that are also configured as router ports in twodifferent subnets.

In accordance with an embodiment, the dual-port virtual router can alsoresolve the issue that a physical link could be mistakenly connected tosome other switch port in the same subnet, or to a switch port that wasnot intended to provide a connection to another subnet. Therefore, themethods and systems described herein also provide a representation ofwhat is on the outside of a subnet.

In accordance with an embodiment, within a subnet, such as subnet A, alocal SM determines a switch port, and then determines a router portconnected to that switch port (e.g., router port 1211 connected, via avirtual link 1223, to switch port 1221). Because the SM sees the routerport 1211 as the end of the subnet that the SM manages, the SM cannotsend discovery and/or management messages beyond this point (e.g., torouter port II 1212).

In accordance with an embodiment, the dual-port virtual router describedabove provides a benefit that the dual-port virtual router abstractionis entirely managed by a management entity (e.g., SM or SMA) within thesubnet that the dual-port virtual router belongs to. By allowingmanagement solely on the local side, a system does not have to providean external, independent management entity. That is, each side of asubnet to subnet connection can be responsible for configuring its owndual-port virtual router.

In accordance with an embodiment, in a situation where a packet, such asan SMP, is addressed to a remote destination (i.e., outside of the localsubnet) arrives local target port that is not configured via thedual-port virtual router described above, then the local port can returna message specifying that it is not a router port.

Many features of the present invention can be performed in, using, orwith the assistance of hardware, software, firmware, or combinationsthereof. Consequently, features of the present invention may beimplemented using a processing system (e.g., including one or moreprocessors).

FIG. 13 shows a method for supporting dual-port virtual router in a highperformance computing environment, in accordance with an embodiment. Atstep 1310, the method can provide at one or more computers, includingone or more microprocessors, a first subnet, the first subnet comprisinga plurality of switches, the plurality of switches comprising at least aleaf switch, wherein each of the plurality of switches comprise aplurality of switch ports, a plurality of host channel adapters, eachhost channel adapter comprising at least one host channel adapter port,a plurality of end nodes, wherein each of the end nodes are associatedwith at least one host channel adapter of the plurality of host channeladapters, and a subnet manager, the subnet manager running on one of theplurality of switches and the plurality of host channel adapters.

At step 1320, the method can configure a switch port of the plurality ofswitch ports on a switch of the plurality of switches as a router port.

At step 1330, the method can logically connect the switch portconfigured as the router port to a virtual router, the virtual routercomprising at least two virtual router ports.

Redundant Fully and Semi-Independent Network

In accordance with an embodiment, a mission critical system should workcorrectly and provide the relevant service with correct data to thecorrect clients at all times within the expected response time andoverall performance constraints defined for the system.

In accordance with an embodiment, for systems implemented as distributedclusters of computers, this also implies that communication between therequired set of computers in the cluster must always be operational.

In accordance with an embodiment, a desirable premise for a networkcommunication system to be operational is that all the physicalconnectivity between components like host adapters and switches iscorrect in terms of that the correct components and connectors areconnected via the correct cables, and that all involved components areconfigured in the correct way.

In accordance with an embodiment, however, since hardware components canfail and operators can and do mistakes, it is critical that nocommunication depends solely on any single point of failure in thenormal case. If a fault or mistake occurs that prevents communicationvia one component and communication path, then it is of paramountimportance that this is detected and that the communication is failedover to an alternative, redundant communication path immediately—or atleast before the non-operational communication path has had anysignificant impact on system operation or response times.

In accordance with an embodiment, also, whenever a fault is present thatleaves some or all current communication vulnerable if a second failureshould ever happen, it is important that relevant repair operations cantake place ASAP and/or that an additional backup solution may be used toprevent total loss of service.

In accordance with an embodiment, another aspect is that since systemand application software is very rarely error free, and also that thereis often a need to enhance the system features over time, it isimportant that it is possible to upgrade the various software componentsin the system without causing any outages. In a distributed clustersystem, this will typically imply a “rolling upgrade” model whereredundant components are upgraded in a strict order so that the systemis always fully operational with the required set of components and therequired communication.

In accordance with an embodiment, also, in order to enhance thecapabilities and/or extend the capacity of a system, physical changes interms of additional HW components and/or replacement of an existing HWcomponent with a more capable one may be required. Such upgrades maythen also imply new software and/or firmware in the system.

However, new software and firmware versions as well as new HW versionsintroduce the risk of introducing new or earlier undetected errors aswell as risk of interoperability problems between differentsoftware/firmware components on the same or between different nodes inthe cluster. Hence, in the ideal case, the ability to operate the systemshould not depend on that only a single type of software is being usedthroughout the system, nor on the successful upgrade from one softwareversion to another. In order to achieve this, one approach is to ensurethat the required service can be implemented in redundant manner by twosets of hardware components of different types and with different setsof software and firmware, and where either no dependency at all existsbetween the different sets of redundant components, or only minimal andextremely well defined and controlled dependency exits.

In accordance with an embodiment, one example of such systems is the useof geographically separate systems implemented by different computertypes and using different software, but where backup data can betransferred between the systems using a neutral format with minimaldependency on either system. A less strict version of this is that aprimary and backup site are using the same type of equipment but are notupgraded at the same time. Hence, typically, the backup site continuesto use version N until sufficient confidence has been established forversion N+1 at the primary site.

In accordance with an embodiment, another approach is to have severalindependent implementations of the same functions operating in parallel.This approach has been used in space missions where multiple versions ofcritical components have been developed by different teams independentlyof each other. A less extreme version of this approach applied to thecluster communication infrastructure would be to have two independentnetworks each implemented by gear (HW and SW/FVV) from differentvendors, but where communication between pairs of computers canfail-over between the two network infrastructures. This approach fornetwork redundancy can then be applied orthogonally to whether differenttypes of computers and host software is used within the cluster in orderto provide similar kinds of independence and redundancy at this levelalso.

In accordance with an embodiment, still, from a pragmatic perspective,cost and complexity are also important factors even when designingmission critical, highly available systems. Hence, different deploymentsmay use different levels of redundancy and different levels of multipleinfrastructure types (i.e. if more than a single) in order to fit thebudget and the risk scenarios for the relevant system deployment.

In accordance with an embodiment, a fully redundant private fabric isstill subject to propagation of management and congestion problems/bugsas well as “disturbance” caused by link failures and reconfigurationfrom one redundant part to the other when implemented as a singlesubnet.

In accordance with an embodiment, in order to provide two (or more)fully or semi-independent fabrics, hosts can comprise redundantconnectivity to each fabric in order to prevent loss of connectivity ifa pair of hosts each have lost a single connection to differentindependent fabrics.

In accordance with an embodiment, a challenge is to provide redundantconnectivity between two fabrics that is independent of the normalmanagement of each fabric and that is used for data communication whenno other option exists.

FIG. 14 shows a system for supporting redundant independent networks ina high performance computing environment, in accordance with anembodiment.

In accordance with an embodiment, two or more rails, such as Rail A 1401and Rail B 1421 can be provided. Although not shown, each independentrail can comprise one or a plurality of interconnected switches, as wellas a multicast proxy (MC Proxy), such as MC Proxy 1402 and MC Proxy1422. In addition, each rail can comprise a highly available pathservice (HAPS), such as HAPS 1403 and HAPS 1423. The rails can beconnected to a number of hosts, such as host 1 1430 through host N 1440.Although not shown, each host can comprise one or more end nodesconnected to the rail via one or more host channel adapters. Inaddition, the end nodes can comprise one or more virtual machines, asdescribed above in relation to virtualized environment (e.g., utilizinga virtual switch, virtual port, or other similar architectures asdescribed above or similar in nature). In accordance with an embodiment,each host can comprise a multi-path selection component, such asMPSelect 1431 and MPSelect 1441.

In accordance with an embodiment, the term “rail” can be used toidentify both, two, or more independent fabrics/subnets as well as theredundant connections/links from hosts. Each rail can provide aredundant, separated, point to point (for unicast), or point to multiplepoints (multicast) traffic between end nodes.

In accordance with an embodiment, Rail A and Rail B can be connected viaone or more inter-rail links (IRL)

In accordance with an embodiment, the term “IRL” (Inter Rail Link) canbe considered of as being similar to an Inter Switch Link (ISL).However, an IRL can be used in a restricted way by not being part ofeither rail.

In accordance with an embodiment, the term “MC Proxy” can refer to aMulticast Proxy. An MC Proxy can comprise a highly available componentthat forwards selected multicast packets from one rail to the other(e.g., ARP (address resolution protocol) requests).

In accordance with an embodiment, the term “HAPS” can refer to a HA(highly available) Path Service. HAPS can comprise a highly availablecomponent that operates within the context of one rail, but communicateswith a peer in the other rail to enable unicast data traffic forwardingvia IRL(s) whenever this is required/requested for two hosts tocommunicate.

In accordance with an embodiment, the term “MPSelect” can refer to ahost based HA/Multi-path logic to select which rail to use for differentconnections to different peer hosts.

In accordance with an embodiment, in a single rack topology, two leafswitches within the rack can represent two rails (i.e., the smallesttopology where two rails are separated by hardware). There can be atleast two IRLs between the Leaf Switches. In the case of an InfiniBandtopology, each Leaf Switch can be a single subnet with an embeddedSubnet Manager that is always the master subnet manager for eachrespective rail.

In accordance with an embodiment, in a multi-rack topology, two Leafswitches in each rack can represent two rails. Each leaf switch in asingle rack represents a different rail. At least one Spine switch ineach rack. The set of spines is divided into two groups—one for eachrail. There can be special handling of dual and 3-rack configuration toavoid single spine is SPOF (single point of failure) in any rail. Leafswitches in one rail are connected to all spines in the same rail (butnot to the other). For M>1 IRLs between two or more pairs of spines fromeach rail. In the case of an InfiniBand topology, redundant SMs can beprovided, located on two or more switches (or possibly dedicated hosts)within each rail

In accordance with an embodiment, in both single rack and multi-racktopologies, Fat-Tree routing can ignore inter rail links. In the case ofan InfiniBand topology, different rails are configured with differentM_Keys (management keys) ensuring no Subnet Managerinteraction/interference across IRLs.

In accordance with an embodiment, a “HA path service” (HAPS) can keeptrack of the complete HCA node and port population in each subnet. (Thismay also include System Image GUID for handling hosts with multiple HCAconfigurations).

In accordance with an embodiment, the HAPS can useGID-in-service/GID-out-of-service event notification from SA or specialprotocol. In the case where the HAPS is implemented as a host basedservice (that may be co-located with MC proxy instance(s)), then nospecial protocol is required by default for keeping track of nodepopulation, but the HAPS will then have a scope that is limited by thepartitions that the relevant HCA port can be member of.

In accordance with an embodiment, a HAPS implementation that isco-located with the master SM can have a more direct interaction withthe SM, and would not be limited to representing only specificpartitions.

In accordance with an embodiment, the HAPS can keep track of switcheswith “cross-link” ports in each L2 subnet and ensure correctconnectivity. This is similar to how an “Inter Subnet Manager” canensure correct connectivity between peer router ports.

In accordance with an embodiment, the HAPS can establish unicast LIDforwarding for “remote LIDs” that require unicast forwarding via crosslink. This can in principle be done “independently” of the master SM inthe relevant L2 subnet. The requirement would be that the SM can beinstructed (configuration policy to use a specific LID range, but stillset up an “LinearFDBTop” value for each switch that is based on aseparate configuration parameter. In this way, the master SM in each L2subnet would be operating on non-overlapping LID ranges, but theswitches in each L2 subnet would still be able to forward unicastpackets with a DLID value in the range belonging to the other(redundant) L2 Subnet.

In accordance with an embodiment, as long as the LID range boundary isaligned on an Linear Forwarding Table (LFT) block boundary, then it ispossible for the HAPS to update LFT blocks to manage the unicast crossconnectivity independently of (and concurrently with) the master SM inthe local subnet. The actual update may be performed directly via SMPoperations, or via a special agent on the switches.

In accordance with an embodiment, an alternative scheme is that the HAPSrequests the local SM to consider the relevant cross link port torepresent all the remote LIDs that are currently required for remoteconnectivity via this cross-link port. (This is similar to handling ofrouter ports, but a router port only requires a single LID that ishandled during the normal subnet discovery/initialization process,whereas this would be a completely new SM operation.)

In accordance with an embodiment, the local Master SM/SA can be providedwith path records for remote PortGlDs that reflects the relevant DLID(similar to how an “Inter Subnet Manager” provides path records forremote ports to the local Master SM in a router based context.) Withoutrouter ports, the SA can then be able to look up path records based onthe supplied info, but can be able to understand that the cross-linkport is the “local destination” in the local subnet.

In accordance with an embodiment, if this unicast cross link handling iscombined with a scheme where no Path Record Query is required (see,e.g., U.S. Patent Application entitled “SYSTEM AND METHOD FOR SUPPORTINGNODE ROLE ATTRIBUTES IN A HIGH PERFORMANCE COMPUTING ENVIRONMENT”,application Ser. No. 15,416,899, filed on Jan. 26, 2017, and U.S. Pat.No. 7,991,006 entitled “Filtering Redundant Packets in Computer NetworkEquipments”, which are herein incorporated by reference), then the localSM/SA does not need to know about paths to remote PortGUIDs at all.

FIG. 15 shows a system for supporting redundant independent networks ina high performance computing environment, in accordance with anembodiment.

In accordance with an embodiment, the figure shows a single rackimplementation for supporting redundant independent networks in a highperformance computing environment.

In accordance with an embodiment, within a single rack topology, therack can comprise two or more leaf switches 1512-13. The rack canadditionally and optionally comprise a number of other switches 1511.These additional switches are optional as the smallest baseconfiguration for a single rack topology are two leaf switches.

In accordance with an embodiment, within a single rack topology with twoleaf switches that are interconnected by a set of Inter Switch Links(ISLs) or intr-rail link (IRLs)), two or more rails can be definedeither through leaf switch partitioning, by assigning each leaf switchto a distinct rail.

In accordance with an embodiment, in the case of no leaf switchpartitioning, depending on switch hardware specific restrictions onpacket buffer allocation and switch HW resource organization in general,there may be restrictions on which port numbers can be used for theISLs.

In accordance with an embodiment, in such a situation, each leaf switch1512 and 1513 represents a separate rail with the ISLs representingIRLs. In the specific case of an InfiniBand fabric, each leaf switchrepresents a single subnet with an embedded subnet manager that is amaster subnet manager.

In accordance with an embodiment, in a situation where ports on eachleaf switch are partitioned in such a way to provide two rails withineach leaf switch, then the total number of ports at each leaf switch aredivided into two partitions, with each partition representing anindependent or semi-independent rail. Within a RoCE fabric partition,there may again be restrictions on which port numbers can be used forISLs. (By default the same set of ports will be used for ISLs in boththe partitioned and not partitioned leaf switch case.)

In accordance with an embodiment, in order to reduce the number ofswitches required for implementing both the RoCE fabric as well asaccess to the client network from the private fabric based system insmaller (e.g. quarter rack) configurations, the leaf switches can bepartitioned (e.g., the ports on the leaf switches) and used to implementthe private RoCE fabric into one physical partition (i.e. set ofphysical ports/connectors) that represents the private RoCE fabric, andanother, non-overlapping partition that represents access to the clientnetwork (e.g. the on-premise data-center network). Hence, each suchphysically partitioned switch can have two non-overlapping sets of portswhere only the set of ports that is dedicated to the private RoCE fabricwill be allowed to represent connectivity within the RoCE fabric (andvice versa).

FIG. 16 shows a system for supporting redundant independent networks ina high performance computing environment, in accordance with anembodiment.

In accordance with an embodiment, in a multi-rack topology, there can beX number of racks, where each rack comprises a number of switches,including at least a leaf switch. In the depicted embodiment, the system1600 comprises X racks, including rack 1 1610, rack 2 1620, rack X-11630, and rack X 1640. Each rack comprises a number of switches: rack 1comprises leaf switches 1612-13 and spine switch 1611, rack 2 comprisesleaf switches 1622-23 and spine switch 1621, rack X-1 comprises leafswitches 1632-33 and spine switch 1631, and rack X comprises leafswitches 1642-43 and spine switch 1641. Each spine switch also isconnected to two inter-rail links, as shown in the figure.

In accordance with an embodiment, in a multi-rack topology, each rackcomprises at least two leaf switches, and where the leaf switches belongto separate rails. In the figure, the rail that each switch belongs tois indicated by either a “1” or a “2” shown in each switch. As well, ina multi-rack topology, there is at least one spine switch in each rack.The set of spine switches is divided into two groups, one for each rail.Leaf switches in one rail are connected to all spine switches of thesame rail, but not to spine switches of a different rail. There can be Mgreater than 1 IRLs between two or more pairs of spine switches fromeach rail. In InfiniBand topologies, redundant subnet managers on two ormore switches (or dedicated hosts) within each rail.

In accordance with an embodiment, each leaf switch in each rack has aset of Up-Links that are distributed among all the Spine switches in thefabric. Depending on switch HW specific restrictions on packet bufferallocation and switch HW resource organization in general, there may berestrictions on which port numbers can be used for Up-Links. Each spineswitch has a number of Down-Links that are distributed between all theLeaf switches in the fabric.

In accordance with an embodiment, as long as the spine switches are onlysupposed to provide Down-Link connectivity, there does not have to beany difference in characteristics among different ports. However, sincenot all Spine ports may be utilized (connected) in a specificconfiguration, there may still be a reason for restricting which portnumbers can be used for Down-Links.

In accordance with an embodiment, in the case of multi-rackconfigurations, there is typically no use of partitioned leaf switches.Whereas, as indicated above, a single rack configuration may or may notuse partitioned Leaf switches. Hence, the fabric definition in the caseof single rack configuration can also include information about whethera leaf switch configuration used is partitioned or not. However, smallermulti-rack configurations that are created based on expanding anexisting single rack configuration may also use partitioned leafswitches within one or more racks.

In accordance with an embodiment, both single rack topologies andmulti-rack topologies can support two different embodiments, namelyfully independent rails and semi-independent rails

In accordance with an embodiment, for a fully independent rail topology,each rail consists of an independent set of switches, and there is noconnectivity between switch ports that belongs to different rails.Typical use case for this is with two or more dual-port adapters perserver.

In accordance with an embodiment, in such a case, each server (e.g.,host) can have redundant connectivity to each rail. Hence, no singlepoint of failure in terms of a single adapter or a single adapter portfor any server may lead to that the corresponding server is NOT able tosend and receive data traffic on any individual fabric rail.

In accordance with an embodiment, if two servers do not both haveconnectivity to at least one common rail, then the pair of servers (orany pair of VMs—one on each of the pair of servers) cannot belong to thesame logical cluster where fabric based communication between thecluster nodes are required.

In accordance with an embodiment, in the case where non-overlappingsub-sets of adapters in each server are connected to non-overlappingsets of rails (i.e. there is no adapter that has ports connecting tomore than one of the non-overlapping sets of rails), then the differentrails are also independent in terms of communication protocols as wellas software and firmware versions including both switch firmware, fabricmanagement software, adapter firmware and adapter driver software.

In accordance with an embodiment, the systems and methods describedherein can additionally support semi-independent rails.

In accordance with an embodiment, in a semi-independent rail topology,each rail consists of an independent set of switches, and there is noconnectivity between switch ports that belong to different rails thatare used for data traffic in the normal case. However, “dormant”physical connectivity may exist between switches in different rails inorder to be used to provide connectivity between pairs of servers thatwould otherwise not be able to communicate because they do not both haveoperational connectivity to the same rail. Such connectivity could beimplemented by IRLs or by other means.

In accordance with an embodiment, typical use-case for thisconfiguration is when each server typically has only a single dual portadapter where each adapter port is connected to a leaf switch in adifferent rail. In this case, any single port/link failure for anyserver will imply that it cannot send or receive data traffic on thecorresponding fabric rail.

In accordance with an embodiment, if two servers do not both haveconnectivity to at least one common rail, then either some of the“dormant” connectivity between switches in different rails can beutilized to re-establish connectivity between this particular pair ofservers, or alternatively, the pair of servers (or any pair of VMs—oneon each of the pair of servers) can NOT belong to the same logicalcluster where fabric based communication between the cluster nodes arerequired.

FIG. 17 shows a system for supporting redundant independent networks ina high performance computing environment, in accordance with anembodiment.

More specifically, the figure shows a dual-rail topology with IRLgateways.

In accordance with an embodiment, two or more rails, such as Rail A 1701and Rail B 1721 can be provided. Although not shown, each independentrail can comprise one or a plurality of interconnected switches, as wellas a multicast proxy (MC Proxy), such as MC Proxy 1702 and MC Proxy1722. In addition, each rail can comprise a highly available pathservice (HAPS), such as HAPS 1703 and HAPS 1723. The rails can beconnected to a number of hosts, such as host 1 1730 through host N 1740.Although not shown, each host can comprise one or more end nodesconnected to the rail via one or more host channel adapters. Inaddition, the end nodes can comprise one or more virtual machines, asdescribed above in relation to virtualized environment (e.g., utilizinga virtual switch, virtual port, or other similar architectures asdescribed above or similar in nature). In accordance with an embodiment,each host can comprise a multi-path selection component, such asMPSelect 1731 and MPSelect 1741.

In accordance with an embodiment, instead of direct switch to switchconnectivity for the inter rail links 1705-1708, there can be provided anumber of gateway instances 1750 and 1752, where each gateway instanceprovides a packet processing engine, 1751 and 1753.

In accordance with an embodiment, a packet processing engine (PPS) canbe provided at nodes in the topology, such as gateway nodes.

In accordance with an embodiment, in order to increase the level ofindependence between redundant fabrics, dual-port high-performancepacket processing engines (PPS) can be used instead of directswitch-switch links for both control and data traffic.

In accordance with an embodiment, these kinds of packet processingengines can be used for additional multiple purposes in a scalable way.These PPS can be used to provide a firewall between different systeminstances. The PPS can be used to provide a gateway to cloud/data-centernetwork to connect different private fabrics. The PPS can be used toprovide a gateway between IB and Enet (Ethernet) based private fabrics.The PPS can be used to provide a gateway between private fabric andclient network.

In accordance with an embodiment, systems and methods can keep track ofphysical and logical connectivity. This can be achieved by leveragingleaf switch monitoring of connected end-ports as well as inter-switchconnectivity. Additionally, systems and methods can make use ofhierarchical query and reporting schemes in order to distribute allrelevant connectivity and aliveness information about all relevant endnodes and ports to all relevant peer nodes. Such reporting can alsoinclude nodes and ports that have full connectivity to local leafswitches but where connectivity in the intermediate fabric is limited.

Additionally, systems and methods can leverage adapter/NICfirmware/driver alive-check schemes to detect and report node death (inaddition to link failures) to reduce/avoid need for additional peer-peerchecks, in addition to facilitating path re-balancing and fail-over.

In accordance with an embodiment, systems and methods can supportmulticast, address resolution and path selection. Idempotent multicastoperations like ARP can be done in parallel on multiple rails. In orderto ensure “at least once” semantics for multicast, either selectivereplication is allowed, or multicast traffic can use an extendedprotocol that allows receivers to process a single MC message only once.Multiple concurrent address resolution requests to the same node can beresponded to by multiple interfaces on different rails and then therequester may select the rail to use for further communication.

FIG. 18 is a flowchart of a method for a redundant independent networkin a high performance computing environment, in accordance with anembodiment.

At step 1810, the method can provide, at a computer comprising one ormore microprocessors, one or more switches, one or more racks, each ofthe one or more racks comprising a set of the one or more switches, eachset of the one or more switches comprising at least a leaf switch, aplurality of host channel adapters, at least one of the plurality ofhost channel adapters comprising a firmware and a processor, and aplurality of hosts.

At step 1820, the method can provision two or more rails, the two ormore rails providing redundant connectivity between the plurality ofhosts.

At step 1830, the method can isolate data traffic between the pluralityof hosts to a rail of the two or more rails.

In accordance with an embodiment, when implementing a highly availablecluster network/fabric it is important that redundancy is implemented ina way that minimizes the risk of problems in one area of the fabric arepropagating to other redundant areas of the fabric.

In accordance with an embodiment, also, when a recovery or fail-overaction is required within the fabric, it is important that such actionsdo not impose a load on either control-plane or data-planeinfrastructure that can cause significant performance or forwardprogress issues.

In accordance with an embodiment, in order to allow the system size toscale and also be compatible with legacy highly available hostcommunication run-time systems, each host can have redundant interfaceconnectivity to the fabric, and each such redundant interface can reachany other interface in the redundant fabric. In particular, this impliesthat if two hosts each are having problems with one interface, then theyshould still be able to communicate using the remaining operationalinterface. Hence, interface redundancy can apply to each individualhost, and does not have any dependency on which interfaces are availableon other hosts.

In accordance with an embodiment, whenever a host interface or a switchfails, it can be possible to re-establish relevant communication withoutany dependency on which interface is used to initiate suchcommunication. This implies that the network level redundancy cannot bebased on two fully independent networks where no packet injected in oneof the networks can be forwarded to the other network. Hence, in orderto support legacy HA communication schemes while maximizing theindependence between redundant networking components, a“semi-independent rail” model can be used.

Goals for the “Semi-Independent” HA Fabric:

In accordance with an embodiment, each redundant host interface shouldconnect to an independent L2 subnet (aka “rail”) in the HA fabric.

In accordance with an embodiment, there can exist a single broadcastdomain across the two L2 subnets that allows ARP requests from a singleinterface to reach all other operational host interfaces independentlyof which L2 subnet each such interface is directly connected to.

In accordance with an embodiment, data traffic (e.g. RDMA) between hostsshould not cross between L2 subnets as long as at least one of the L2subnets has at least one connected and operational interface for each ofthe hosts.

In accordance with an embodiment, whenever any pair of hosts that needto communicate are not both able to establish data traffic betweeninterfaces on a single L2 subnet, then a path between the L2 subnetsshould be established for the needed data traffic between the relevanthosts.

In accordance with an embodiment, the host stacks on each host can beable to easily determine which interface to use for communication with aspecific other host, —even if the default decision on each hostsinvolves a different “rail”.

In accordance with an embodiment, in the case of InfiniBand, it shouldnot be possible for hosts to initiate SA requests that cross L2 subnetboundaries.

In accordance with an embodiment, it should not be possible for hosts tocause congestion spreading from one L2 subnet to the other.

Specific Implementation Aspects for InfiniBand Fabric:

HA Path Service (HAPS):

In accordance with an embodiment, a “HA path service” (HAPS) can keeptrack of the complete HCA node and port population in each subnet. (Thismay also include System Image GUID for handling hosts with multiple HCAconfigurations).

In accordance with an embodiment, the HAPS can useGID-in-service/GID-out-of-service event notification from SA or specialprotocol. In the case where the HAPS is implemented as a host basedservice (that may be co-located with MC proxy instance(s)), then nospecial protocol is required by default for keeping track of nodepopulation, but the HAPS will then have a scope that is limited by thepartitions that the relevant HCA port can be member of.

In accordance with an embodiment, a HAPS implementation that isco-located with the master SM can have a more direct interaction withthe SM, and would not be limited to representing only specificpartitions.

In accordance with an embodiment, the HAPS can keep track of switcheswith “cross-link” ports in each L2 subnet and ensure correctconnectivity. This is similar to how an “Inter Subnet Manager” canensure correct connectivity between peer router ports.

In accordance with an embodiment, the HAPS can establish unicast LIDforwarding for “remote LIDs” that require unicast forwarding via crosslink. This can in principle be done “independently” of the master SM inthe relevant L2 subnet. The requirement would be that the SM can beinstructed (configuration policy to use a specific LID range, but stillset up an “LinearFDBTop” value for each switch that is based on aseparate configuration parameter. In this way, the master SM in each L2subnet would be operating on non-overlapping LID ranges, but theswitches in each L2 subnet would still be able to forward unicastpackets with a DLID value in the range belonging to the other(redundant) L2 Subnet.

In accordance with an embodiment, as long as the LID range boundary isaligned on an Linear Forwarding Table (LFT) block boundary, then it ispossible for the HAPS to update LFT blocks to manage the unicast crossconnectivity independently of (and concurrently with) the master SM inthe local subnet. The actual update may be performed directly via SMPoperations, or via a special agent on the switches.

In accordance with an embodiment, an alternative scheme is that the HAPSrequests the local SM to consider the relevant cross link port torepresent all the remote LIDs that are currently required for remoteconnectivity via this cross-link port. (This is similar to handling ofrouter ports, but a router port only requires a single LID that ishandled during the normal subnet discovery/initialization process,whereas this would be a completely new SM operation.)

In accordance with an embodiment, the local Master SM/SA can be providedwith path records for remote PortGIDs that reflects the relevant DLID(similar to how an “Inter Subnet Manager” provides path records forremote ports to the local Master SM in a router based context.) Withoutrouter ports, the SA can then be able to look up path records based onthe supplied info, but can be able to understand that the cross-linkport is the “local destination” in the local subnet.

In accordance with an embodiment, if this unicast cross link handling iscombined with a scheme where no Path Record Query is required, then thelocal SM/SA does not need to know about paths to remote PortGUIDs atall.

Identification and Handling of “Cross-Link” Ports:

In accordance with an embodiment, by default, the redundant InfiniBandL2 subnets can be set up with non-overlapping M_Key ranges prior to thatany cross link connectivity would be provided and/or prior to any SMsbeing active in either L2 subnet. In this way, the SMs in each redundantsubnet would not try to discover or configure anything beyond the switchport in the local subnet connecting to the neighbor redundant subnet.

In accordance with an embodiment, it is not expected that an existingoperational single subnet based system can be converted into a dual L2subnet configuration without significant interruption of normaloperation. Hence, the expectation is that this kind of re-configurationwill take place in a maintenance window where the system services arenot expected to be operational.

In accordance with an embodiment, using Vendor Specific SMA attributes,it will also be possible to establish a protocol that enables explicitconfiguration of a switch as belonging to a specific redundant L2subnet, as well as which switch port numbers are supposed to representcross-link connectivity to the peer redundant L2 subnet.

In accordance with an embodiment, use of Vendor Specific SMA attributeswould be similar to how an “Inter Subnet Manager” handles virtual routerports. However, since no router port or port virtualization exists inthis context, the implementation will be quite different.

In accordance with an embodiment, based on detailed configuration infoand possibly reliance on node-description sub strings, it would bepossible to identify and handle cross-link ports also without use of thespecial Vendor Specific SMA attributes, but this would be more complexand also more exposed to configuration errors.

Specific Implementation Aspects for Ethernet (Private) Fabric:

In accordance with an embodiment, redundancy within interconnect fabricsshould as much as possible ensure that failures/problems in oneredundant part do not propagate to other parts. Ultimately this impliesphysically and logically independent infrastructures. However, the costof this is that either each node can have redundant connectivity to eachsuch independent fabric, or else the ability to recover connectivitybetween two or more servers each with a single link problem issignificantly reduced. By utilizing new ways to provide Ethernet linkconnectivity between two independent subnets without impacting themanagement or fault containment for each individual subnet, it ispossible to address both goals at the same time.

In accordance with an embodiment, the Ethernet private fabric can beimplemented using a conventional Ethernet unicast forwarding scheme withcombination of spanning tree and link aggregation variants, or it can beimplemented using explicit forwarding of individual unicast destinationaddresses in the same way as forwarding of IB packets within a single IBsubnet is implemented.

In accordance with an embodiment, in the case of explicit forwarding ofindividual unicast addresses, the high-level scheme is the following:

In accordance with an embodiment, the complete topology in terms ofport-port connectivity between switch-ports and between switch ports andend-ports is collected from the relevant set of switches. (Optimizationsmay include only collecting topology deltas following an initial fulldiscovery.)

In accordance with an embodiment, the topology information istransformed into a format that can be handled by the same routing logic(aka routing engine) that is used for a corresponding InfiniBand fabric.

In accordance with an embodiment, the routing engine uses the topologyalong with (e.g. VLAN) policy for which physical end ports are allowedto communicate (as well as other relevant optimization and balancingcriteria similar to the IB fabric case) and produces a list of end-portaddress to port mapping tuples for each switch instance in the topology.

In accordance with an embodiment, the resulting (delta) forwarding entrylists are distributed to the switches (i.e. the ones that need updates).

In accordance with an embodiment, multicast can in any case beimplemented using legacy Ethernet schemes for both end-port membershiphandling and forwarding of MC packets.

Multicast Proxy Service:

In accordance with an embodiment, the same/similar considerations as forthe InfiniBand case applies. If the L2 source address in the proxied MCpacket is not the same as the corresponding ARP request “sender hardwareaddress”, then the ARP request may be discarded, or the generation ofunicast ARP response may result in an incorrect L2 destination address.As in the InfiniBand case, in order to avoid dependency on special hoststack handling, the best approach is that the proxy is able to send outthe proxied MC packet with a source L2 address that corresponds to theoriginal sender in the other L2 subnet.

HA Path Service (HAPS):

In accordance with an embodiment, the “HA path service”—HAPS can keeptrack of the complete end port population in each subnet.

In accordance with an embodiment, the ports that belong to the same NICor same host can be correlated between the two subnets.

In accordance with an embodiment, as in the IB case, the situation wherepairs of hosts are only able to communicate if the relevant unicasttraffic is forwarded via cross-links between the two subnets can beidentified.

In accordance with an embodiment, in the case where explicit end-portaddress forwarding is used for unicast traffic then the handling will bevery similar to the IB case. However, in the case of legacy Ethernetunicast forwarding, and in the general case, this may require a proxytype gateway function also for unicast traffic.

In accordance with an embodiment, since the unicast forwarding within anEthernet fabric is based on MACs, then there is no restriction on MACranges used for the various L2 subnets. —The only restriction is thateach host port should have a MAC that is at least unique within therelevant site/domain. In the case of a private fabric, the relevantdomain is then the two redundant L2 subnets.

In accordance with an embodiment, in the case where switches can performforwarding based on either L2 and/or L3 addresses, it would also bepossible to use forwarding based on L3 (IP) addresses instead of L2MACs.

Identification and Handling of “Cross-Link” Ports:

In accordance with an embodiment, based on that individual switches areconfigured to belong to different “rails” combined with the neighborconnectivity info from each switch, it is possible to identify bothswitch-switch connectivity that belongs to the same rail/subnet (fattree) topology as well as intended (or accidental . . . ) cross-linkconnectivity.

In accordance with an embodiment, the cross-link connectivity will thennever be considered for the normal forwarding of either unicast ormulticast connectivity, but the intended cross-connectivity will be usedfor backup inter-rail paths in the case of explicit end-port addressforwarding. As pointed out above, the use of cross-links when legacyEthernet unicast forwarding schemes are being used would in generalrequire proxy/gateway functions for both multicast and unicastforwarding between different rails.

In accordance with an embodiment, when configuring Ethernet switches andNICs for RoCE based RDMA traffic, the relevant links are usuallyconfigured in “loss-less” mode where the down-stream switch or NIC portwill generate “pause frames” to the up-stream sending switch or NIC portwhenever the available packet receive buffer capacity is below a certainthreshold. The sending port will then stop (pause) sending more packetson the relevant priority (if any) until the down-stream port again hasbuffer capacity above a certain threshold.

In accordance with an embodiment, as with other networking technologywhere packet flow control can lead to back pressure throughout thenetwork, a lossless RoCE fabric topology must be routed in a deadlockfree manner. Also, flows that are supposed to have forward progressindependently of each other must use different priorities.

In accordance with an embodiment, in the case of dual-rail topologies,it makes sense to ensure that only the internal topology of a singlerail must be considered in terms of deadlock freedom. By configuringcross links as “lossy” (i.e. down-stream switch ports will not sendpause frames), it is possible to provide deadlock free routing of thetopology in each rail without considering the topology in the rail(s)connected by the cross links. Instead, cross link ports will beconsidered end-ports within the local rail from a deadlock free routingperspective, and hence they cannot be part of any cycle dependency thatcould lead to deadlock.

In accordance with an embodiment, the lossless cross link configurationwill also imply that no congestion in one rail will spread over to theother rail. Hence, a key requirement for independence between theredundant rails is thereby fulfilled.

Using IB Routing Algorithms in Ethernet Fabrics

In accordance with an embodiment, InfiniBand based fabricimplementations utilize complete discovery of connectivity within asubnet by a central master Subnet Manager and subsequent routing basedon a holistic evaluation of the connectivity and then subsequentgeneration of forwarding table contents for all switches in the subnetin order to provide full connectivity among all end-ports that areallowed to communicate.

In accordance with an embodiment, Ethernet based fabric implementations(e.g., RoCE) typically have a more dynamic learning approach forpopulating forwarding tables and rely on distributed algorithms foravoiding forwarding loops. However, such algorithms typically used forestablishing forwarding setup within an Ethernet network do not takeinto account that both forwarding loops and indirect dependency loopsmust be avoided in order to ensure correct forwarding when also takingflow-controlled, loss-less packet traffic into account.

In accordance with an embodiment, by utilizing the ability to collectneighbor information from all switches in an Ethernet fabric, it ispossible to generate a topology representation that can be used by thevarious routing engines provided by a management entity, such as anInfiniBand Subnet Manager.

In accordance with an embodiment, as a result, an Ethernet fabricconfigured to operate in loss-less mode can have internal forwardingtables set up to comply with deadlock avoidance criteria as well asvarious load balancing and optimization criteria used in InfiniBandfabrics.

In accordance with an embodiment, another difference betweenintra-subnet (layer 2) forwarding within IB switches and thecorresponding function in Ethernet switches is that the IB subnet isalways well defined in terms of that all switches and end-ports arealways well known by the IB Subnet Manager and have been assigned wellknown layer 2 addresses (LIDs) before a new intra-subnet routing isapplied. Also, the Subnet Manager ensures that all involved switches canrepresent all required end-port L2 addresses before a new end-port isallowed to be included in an operational subnet.

In accordance with an embodiment, in Ethernet switches on the otherhand, new end ports and the corresponding L2 (or L3) addresses may beobserved and learned dynamically by the various switches. Also, Ethernetswitches may not have forwarding tables that allows each individualrelevant end-port address to be represented concurrently. Instead, anEthernet switch may operate its forwarding table as a cache and onlyinclude a subset of the relevant addresses and perform replacement basedon caching algorithms like “most frequently used”, “most recently used”etc. Further, when a packet is received that does not have itsdestination address cached in the local forwarding table, the switch may“flood” the packet by broadcasting it out on all legal egress ports inorder to try to ensure that the packet can be delivered to the intendedreceiver despite the lack of local forwarding table capacity.

In accordance with an embodiment, in the case of high performance RDMAtraffic, dynamic address learning and flooding is typically notacceptable for performance reasons in the general case. Also, Ethernetswitches typically support both L2 and L3 based address forwarding andsupport forwarding table sizes that allow tens of thousands ofindividual end port L2 and/or L3 addresses to be representedconcurrently.

In accordance with an embodiment, in the case of a dedicated Ethernetfabric for RoCE based RDMA communication using modern switches, it isreasonable to expect that all the involved switches can represent allrelevant end-port addresses in their forwarding tables.

In accordance with an embodiment, further, Ethernet switches provideinterface support for SDN (Software Defined Networking) basedmanagement, which in particular includes the ability to control theswitch forwarding tables from an external SDN controller (i.e. amanagement software entity running on some trusted host or managementserver with access to the switches in the relevant network/fabric).

Implementation:

In accordance with an embodiment, an implementation includes three mainmodules, a topology provider (TP), a routing engine (RE), and a switchinitializer (SI).

In accordance with an embodiment, the three modules can be implementedas a single application running in the context of a single process or astwo or more independent processes on one or more communicating networknodes. However, in all cases the roles and interfaces for the variousmodules can be according to the following:

In accordance with an embodiment, the TP can use a combination ofvarious in-band and out-of-band methods for discovering the completeEthernet fabric. The basis for this may be a list of switches that aresupposed to be present in the fabric as well as the relevant accessmethods and addresses for these switches. The TP can use SNMP access tothe switches in order to query relevant Management Information Bases(MIBs) representing neighbor port information obtained via LLDP (LinkLayer Discovery Protocol) in addition to information about local linkstates. Also, the TP can register to receive SNMP trap (event) messagesin order to be asynchronously informed about any change in either locallink state or identity of directly connected neighbor ports. In thisway, the TP can both keep track of all direct connectivity for all knownswitches, but can also detect cases where a connected switch is not aswitch defined to be part of the fabric configuration. In such cases theTP can report the issue so that the unexpected switch can either beincluded in the defined set of switches for the fabric configuration, orthe physical cabling between the switches can be corrected accordingly.

In accordance with an embodiment, the TP can initially perform acomplete discovery of the fabric and can then assign logical identifiers(LIDs) to the various components in the same way as a Subnet Managerwould assign LIDs to all switches and end-ports in an InfiniBand subnet.The TP can ensure that the connectivity of the fabric is in accordancewith a defined policy before allowing the whole fabric to becomeoperational, or unexpected or illegal connectivity or nodes may beexcluded from the topology before deciding to initiate routing andinitialization of the topology.

In accordance with an embodiment, a representation of the completetopology with the assigned LIDs can then be handed over to the RE thatwould then perform a routing algorithm on the provided topology based oncurrent policy about routing. The actual representation of the topologyas well as the implementation of the routing algorithm may beconstructed so that the same source code as is used by an IB SubnetManager for the relevant routing algorithm is also used by the RE for anEthernet fabric. In this way it can be ensured that a single version ofthe routing algorithm can be maintained and re-used for both InfiniBandand Ethernet fabrics.

In accordance with an embodiment, the RE will generate output in termsof a forwarding table for each switch in the topology where theforwarding table is indexed by the LID of the relevant end-port andwhere the contents of the corresponding forwarding table entry is theswitch port number of the local switch port that should be the egressport for unicast packets sent to the corresponding end-port.

In accordance with an embodiment, the SI will receive the forwardingtables from the RE and will then translate the information into whateveraddress representation is supposed to be used in the relevant Ethernetfabric (i.e. either L2 or L3 addresses). The SI will then use relevant(e.g. SDN type) management interfaces on the relevant switches viaeither in-band or out-of-band access methods to update the switchforwarding tables to represent the intended routing generated by the RE.

In accordance with an embodiment, when the connectivity of the fabricchanges, the TP will discover this via either receiving event messagesfrom the switches, and/or by performing periodic monitoring of the stateof the switches. Based on the observed topology delta, it will thengenerate a new topology representation that the RE can use to generatenew forwarding tables that the SI in its turn can use to update theswitches. Depending on the capabilities of the routing algorithmimplementation, the RE may always generate a complete new routing basedon the complete new topology information, or it may generate a minimalupdate including only the necessary changes reflecting the delta betweenthe earlier and the new topology generation.

FIG. 19 shows a system for using InfiniBand (IB) routing algorithms forEthernet fabrics in a high performance computing environment, inaccordance with an embodiment.

In accordance with an embodiment, a system 1900 can comprise a number ofEthernet switches, 1930-1931, 1920-1923, and a number of nodes 1901-1906which are interconnected via the switches.

In accordance with an embodiment, the system can additionally comprise anumber of modules, such as a topology provider (TP) 1940, a routingengine (RE) 1941, and a switch initializer (SI) 1942. Although shown asbeing separate from the switches and nodes, these modules can variouslybe hosted at the shown hardware, or hosted on separate machines capableof managing the system 1900.

In accordance with an embodiment, the TP can use a combination ofvarious in-band and out-of-band methods for discovering the completeEthernet fabric. The basis for this may be a list of switches that aresupposed to be present in the fabric as well as the relevant accessmethods and addresses for these switches.

In accordance with an embodiment, the TP can initially perform acomplete discovery of the fabric 1900 and then assign logical/localidentifiers (LIDs) to the various components (switches and nodes). TheTP can ensure that the connectivity of the fabric is in accordance withdefined policy before allowing the whole fabric to become operational,or unexpected or illegal connectivity or nodes may be excluded from thetopology before deciding to initiate routing and initialization of thetopology.

In accordance with an embodiment, a representation of the completetopology with the assigned LIDs can then be handed over to the RE 1941that performs a routing algorithm on the representation based on acurrent (or configurable) policy about routing. The actualrepresentation of the topology as well as the implementation of therouting algorithm may be constructed so that the same source code as isused by an IB Subnet Manager for the relevant routing algorithm is alsoused by the RE for an Ethernet fabric. In this way it can be ensuredthat a single version of the routing algorithm can be maintained andre-used for both InfiniBand and Ethernet fabrics.

In accordance with an embodiment, the RE will generate output in termsof a forwarding table for each switch in the topology where theforwarding table is indexed by the LID of the relevant end-port andwhere the contents of the corresponding forwarding table entry is theswitch port number of the local switch port that should be the egressport for unicast packets sent to the corresponding end-port.

In accordance with an embodiment, the SI 1942 can receive the forwardingtables from the RE and can then translate the information into whateveraddress representation is supposed to be used in the relevant Ethernetfabric (i.e. either L2 or L3 addresses). The SI will then use relevant(e.g. SDN (software defined network) type) management interfaces on therelevant switches via either in-band or out-of-band access methods toupdate the switch forwarding tables to represent the intended routinggenerated by the RE.

FIG. 20 is a flowchart of a method for using InfiniBand routingalgorithms for Ethernet fabrics in a high performance computingenvironment.

At step 2010, the method can provide, at a computer, the computercomprising one or more microprocessors, a first Ethernet fabricoperating in loss-less mode, the first Ethernet fabric comprising aplurality of Ethernet switches, a plurality of hosts interconnected viathe plurality of Ethernet switches, a topology provider (TP) module, arouting engine (RE) module, and a switch initializer (SI) module.

At step 2020, the method can perform, by the topology provider, adiscovery sweep of the plurality of hosts and the plurality of switchesand assigns an address to each of the plurality of hosts and theplurality of switches.

At step 2030, the method can calculate, by the routing engine, a routingmap, based upon a routing scheme, for the plurality of hosts and theplurality of switches, the routing map comprising a plurality offorwarding tables.

At step 2040, the method can configure, by the switch initializer, eachof the plurality of switches with a forwarding table of the plurality offorwarding tables calculated by the routing engine.

On-Demand Unicast Forwarding

In accordance with an embodiment, when any specific host is notavailable via any interface directly connected to a local subnet, thiscan be recorded by a “HA Path Service”. The HA Path Service may beco-located with a multicast proxy service, and multiple instances may beresponsible for different sets of logical networks.

In accordance with an embodiment, the HA Path Service can additionallybe implemented as a switch based function (e.g., in the case ofInfiniBand-based network, the HA Path Service could be co-located with,and could cooperate with a local master subnet manager). In this casethe local HA Path Service can communicate with a peer in the other L2subnet (e.g., another HA path service in another rail).

In accordance with an embodiment, the HA Path Service can track, andrecord at an associated memory or storage, which hosts/end points arecurrently available via interface(s) to only one of the local L2subnets, and whenever there exists two or more hosts that do not sharedirect access to the same L2 subnet, and that also are members of thesame L2 logical links/subnets (e.g. VLANs/Partitions), then unicastpaths can be set up that allows communication between a relevant set ofhost interfaces in one subnet and the relevant set of host interfaces inthe other subnet. Such unicast paths can, for example, be established onan inter-rail link.

In accordance with an embodiment, such paths will be implemented bysetting up forwarding for the relevant interface addresses (e.g.MACs/LIDs) via switch ports in each local L2 subnet that are connectedto a switch port in the other L2 subnet.

In accordance with an embodiment, in the case of switches that canhandle either L2 or L3 address based forwarding, it is also possible touse either of L2 or L3 as well as combinations for this specialforwarding.

In accordance with an embodiment, the switch-switch connectivity betweenthe L2 subnets will be handled in such a way that such connectivity isnot considered by the normal L2 subnet internal discovery and routing.

FIG. 21 shows a system for on-demand unicast forwarding in a highperformance computing environment, in accordance with an embodiment.

In accordance with an embodiment, two or more rails, such as Rail A 1401and Rail B 1421 can be provided. Although not shown, each independentrail can comprise one or a plurality of interconnected switches, as wellas a multicast proxy (MC Proxy), such as MC Proxy 1402 and MC Proxy1422. In addition, each rail can comprise a highly available pathservice, or a high availability path service, (HAPS), such as HAPS 1403and HAPS 1423. Each of the HAPS can be associated with, or have accessto (both read and write) a memory, such as memory 2101 and memory 2111.The rails can be connected to a number of hosts, such as host 1 1430through host N 1440. Although not shown, each host can comprise one ormore end nodes connected to the rail via one or more host channeladapters. In addition, the end nodes can comprise one or more virtualmachines, as described above in relation to virtualized environment(e.g., utilizing a virtual switch, virtual port, or other similararchitectures as described above or similar in nature). In accordancewith an embodiment, each host can comprise a multi-path selectioncomponent, such as MPSelect 1431 and MPSelect 1441.

In accordance with an embodiment, the term “rail” can be used toidentify both, two, or more independent fabrics/subnets as well as theredundant connections/links from hosts. Each rail can provide aredundant, separated, point to point (for unicast), or point to multiplepoints (multicast) traffic between end nodes.

In accordance with an embodiment, Rail A and Rail B can be connected viaone or more inter-rail links (IRL), such as IRL 1 1405 and IRL 2 1406.

In accordance with an embodiment, the term “IRL” (Inter Rail Link) canbe considered of as being similar to an Inter Switch Link (ISL).However, an IRL can be used in a restricted way by not being part ofeither rail.

In accordance with an embodiment, the term “MC Proxy” can refer to aMulticast Proxy. An MC Proxy can comprise a highly available componentthat forwards selected multicast packets from one rail to the other(e.g., ARP (address resolution protocol) requests).

In accordance with an embodiment, the term “HAPS” can refer to a HA(high availability) Path Service. HAPS can comprise a highly availablecomponent that operates within the context of one rail, but communicateswith a peer in the other rail to enable unicast data traffic forwardingvia IRL(s) whenever this is required/requested for two hosts tocommunicate, such as via communication 2120.

In accordance with an embodiment, the term “MPSelect” can refer to ahost based HA/Multi-path logic to select which rail to use for differentconnections to different peer hosts.

In accordance with an embodiment, in a single rack topology, two leafswitches within the rack can represent two rails (i.e., the smallesttopology where two rails are separated by hardware). There can be atleast two IRLs between the Leaf Switches. In the case of an InfiniBandtopology, each Leaf Switch can be a single subnet with an embeddedSubnet Manager that is always the master subnet manager for eachrespective rail.

In accordance with an embodiment, in a multi-rack topology, two Leafswitches in each rack can represent two rails. Each leaf switch in asingle rack represents a different rail. At least one Spine switch ineach rack. The set of spines is divided into two groups—one for eachrail. There can be special handling of dual and 3-rack configuration toavoid single spine is SPOF (single point of failure) in any rail. Leafswitches in one rail are connected to all spines in the same rail (butnot to the other). For M>1 IRLs between two or more pairs of spines fromeach rail. In the case of an InfiniBand topology, redundant SMs can beprovided, located on two or more switches (or possibly dedicated hosts)within each rail

In accordance with an embodiment, in both single rack and multi-racktopologies, Fat-Tree routing can ignore inter rail links. In the case ofan InfiniBand topology, different rails are configured with differentM_Keys (management keys) ensuring no Subnet Managerinteraction/interference across IRLs.

In accordance with an embodiment, a “HA path service” (HAPS) can keeptrack of the complete HCA node and port population in each subnet. (Thismay also include System Image GUID for handling hosts with multiple HCAconfigurations).

In accordance with an embodiment, the HAPS can useGID-in-service/GID-out-of-service event notification from SA or specialprotocol. In the case where the HAPS is implemented as a host basedservice (that may be co-located with MC proxy instance(s)), then nospecial protocol is required by default for keeping track of nodepopulation, but the HAPS will then have a scope that is limited by thepartitions that the relevant HCA port can be member of.

In accordance with an embodiment, a HAPS implementation that isco-located with the master SM can have a more direct interaction withthe SM, and would not be limited to representing only specificpartitions.

In accordance with an embodiment, the HAPS can keep track of switcheswith “cross-link” ports in each L2 subnet and ensure correctconnectivity. This is similar to how an “Inter Subnet Manager” canensure correct connectivity between peer router ports.

In accordance with an embodiment, the HAPS can establish unicast LIDforwarding for “remote LIDs” that require unicast forwarding via crosslink. This can in principle be done “independently” of the master SM inthe relevant L2 subnet. The requirement would be that the SM can beinstructed (configuration policy to use a specific LID range, but stillset up an “LinearFDBTop” value for each switch that is based on aseparate configuration parameter. In this way, the master SM in each L2subnet would be operating on non-overlapping LID ranges, but theswitches in each L2 subnet would still be able to forward unicastpackets with a DLID value in the range belonging to the other(redundant) L2 Subnet.

In accordance with an embodiment, as long as the LID range boundary isaligned on an Linear Forwarding Table (LFT) block boundary, then it ispossible for the HAPS to update LFT blocks to manage the unicast crossconnectivity independently of (and concurrently with) the master SM inthe local subnet. The actual update may be performed directly via SMPoperations, or via a special agent on the switches.

In accordance with an embodiment, an alternative scheme is that the HAPSrequests the local SM to consider the relevant cross link port torepresent all the remote LIDs that are currently required for remoteconnectivity via this cross-link port. (This is similar to handling ofrouter ports, but a router port only requires a single LID that ishandled during the normal subnet discovery/initialization process,whereas this would be a completely new SM operation.)

In accordance with an embodiment, the local Master SM/SA can be providedwith path records for remote PortGlDs that reflects the relevant DLID(similar to how an “Inter Subnet Manager” provides path records forremote ports to the local Master SM in a router based context.) Withoutrouter ports, the SA can then be able to look up path records based onthe supplied info, but can be able to understand that the cross-linkport is the “local destination” in the local subnet.

In accordance with an embodiment, both of the HAPS displayed in FIG. 21can track, and record at the respective associated memory 2101 and 2111,which hosts/end points are currently available via interface(s) to onlyone of the local subnets (i.e., Rail A and Rail B in the figure). Inaddition, by tracking such connectivity, the HAPS can additionallydetermine when two or more hosts, which were previously incommunication, lose such communication (due to, for example, a switcherror or the like). In such situations, then the HAPS of the two railscan set up communication 2120 such that unicast packets can still besent to the two or more hosts that were previously in communication,where the new unicast communication can take place via one or more ofthe inter-rail links. This then provides a way for unicast paths to beset up that allows communication between a relevant set of hostinterfaces in one subnet and the relevant set of host interfaces in theother subnet.

In accordance with an embodiment, a decision to start using inter-raillinks for unicast traffic between one or more pairs of end nodes can bebased upon, for example, a decision tree or a similar method. At thestart, a HAPS can detect a change in, for example, connectivity (e.g.,physical connectivity) in any of the rails so that physical connectivityin any of the rails is lost. Then, the HAPS can determine if the changein physical connectivity has disrupted communication of any pair ofnodes that are allowed to communicate, and are no longer able tocommunicate on either rail due to the change in connectivity. Then, forat least one of the pairs (two or more) of end nodes (i.e., hosts) thatwere previously able to communicate, but now that cannot communicate oneither rail, but where each node of the pair node has access to at leastone of the rails, the HAPS can establish a unicast forwarding via one ormore of the inter-rail links.

In accordance with an embodiment, a decision to stop using inter-raillinks for unicast traffic between one or more pairs of nodes can bebased upon, for example, a decision tree or a similar method. At thestart, the HAPS can determine when physical connectivity status changesin any of the rails so that physical connectivity is added orre-established. The HAPS can additionally determine if the change inphysical connectivity has provided that any pair of nodes that arecurrently using inter-rail links for communication is now able tocommunicate on either rail without any IRL dependency. Then, for allsuch pairs of nodes that can now communicate on either rail, the HAPScan remove relevant unicast forwarding via the IRLs.

In accordance with an embodiment, while the above description refers toonly a singular HAPS, one or ordinary skill in the art would appreciatethat the respective HAPS in various rails can communicate with eachother in negotiating the enablement and disablement of unicastforwarding over the one or more inter-rail links.

FIG. 22 shows a system for on-demand unicast forwarding in a highperformance computing environment, in accordance with an embodiment.

More specifically, the figure shows a system for on-demand unicastforwarding in a dual-rail topology with IRL gateways.

In accordance with an embodiment, two or more rails, such as Rail A 1701and Rail B 1721 can be provided. Although not shown, each independentrail can comprise one or a plurality of interconnected switches, as wellas a multicast proxy (MC Proxy), such as MC Proxy 1702 and MC Proxy1722. In addition, each rail can comprise a highly available pathservice (HAPS), such as HAPS 1703 and HAPS 1723. Each of the HAPS can beassociated with, or have access to (both read and write) a memory, suchas memory 2201 and memory 2211. HAPS can comprise a highly availablecomponent that operates within the context of one rail, but communicateswith a peer in the other rail to enable unicast data traffic forwardingvia IRL(s) whenever this is required/requested for two hosts tocommunicate, such as via communication 2220. The rails can be connectedto a number of hosts, such as host 1 1730 through host N 1740. Althoughnot shown, each host can comprise one or more end nodes connected to therail via one or more host channel adapters. In addition, the end nodescan comprise one or more virtual machines, as described above inrelation to virtualized environment (e.g., utilizing a virtual switch,virtual port, or other similar architectures as described above orsimilar in nature). In accordance with an embodiment, each host cancomprise a multi-path selection component, such as MPSelect 1731 andMPSelect 1741.

In accordance with an embodiment, instead of direct switch to switchconnectivity for the inter rail links 1705-1708, there can be provided anumber of gateway instances 1750 and 1752, where each gateway instanceprovides a packet processing engine, 1751 and 1753.

In accordance with an embodiment, a packet processing engine (PPS) canbe provided at nodes in the topology, such as gateway nodes.

In accordance with an embodiment, in order to increase the level ofindependence between redundant fabrics, dual-port high-performancepacket processing engines (PPS) can be used instead of directswitch-switch links for both control and data traffic.

In accordance with an embodiment, these kinds of packet processingengines can be used for additional multiple purposes in a scalable way.These PPS can be used to provide a firewall between different systeminstances. The PPS can be used to provide a gateway to cloud/data-centernetwork to connect different private fabrics. The PPS can be used toprovide a gateway between IB and Enet (Ethernet) based private fabrics.The PPS can be used to provide a gateway between private fabric andclient network.

In accordance with an embodiment, systems and methods can keep track ofphysical and logical connectivity. This can be achieved by leveragingleaf switch monitoring of connected end-ports as well as inter-switchconnectivity. Additionally, systems and methods can make use ofhierarchical query and reporting schemes in order to distribute allrelevant connectivity and aliveness information about all relevant endnodes and ports to all relevant peer nodes. Such reporting can alsoinclude nodes and ports that have full connectivity to local leafswitches but where connectivity in the intermediate fabric is limited.

Additionally, in accordance with an embodiment, systems and methods canleverage adapter/NIC firmware/driver alive-check schemes to detect andreport node death (in addition to link failures) to reduce/avoid needfor additional peer-peer checks, in addition to facilitating pathre-balancing and fail-over.

In accordance with an embodiment, systems and methods can supportmulticast, address resolution and path selection. Idempotent multicastoperations like ARP can be done in parallel on multiple rails. In orderto ensure “at least once” semantics for multicast, either selectivereplication is allowed, or multicast traffic can use an extendedprotocol that allows receivers to process a single MC message only once.Multiple concurrent address resolution requests to the same node can beresponded to by multiple interfaces on different rails and then therequester may select the rail to use for further communication.

In accordance with an embodiment, both of the HAPS displayed in FIG. 22can track, and record at the respective associated memory 2201 and 2211,which hosts/end points are currently available via interface(s) to onlyone of the local subnets (i.e., Rail A and Rail B in the figure). Inaddition, by tracking such connectivity, the HAPS can additionallydetermine when two or more hosts, which were previously incommunication, lose such communication (due to, for example, a switcherror or the like). In such situations, then the HAPS of the two railscan communicate 2220 such that unicast packets can still be sent to thetwo or more hosts that were previously in communication, where the newunicast communication can take place via one or more of the inter-raillinks. This then provides a way for unicast paths to be set up thatallows communication between a relevant set of host interfaces in onesubnet and the relevant set of host interfaces in the other subnet.

In accordance with an embodiment, a decision to start using inter-raillinks for unicast traffic between one or more pairs of end nodes can bebased upon, for example, a decision tree or a similar method. At thestart, a HAPS can detect a change in, for example, connectivity (e.g.,physical connectivity) in any of the rails so that physical connectivityin any of the rails is lost. Then, the HAPS can determine if the changein physical connectivity has disrupted communication of any pair ofnodes that are allowed to communicate, and are no longer able tocommunicate on either rail due to the change in connectivity. Then, forat least one of the pairs (two or more) of end nodes (i.e., hosts) thatwere previously able to communication, but now that cannot communicateon either rail, but where each node of the pair node has access to atleast one of the rails, the HAPS can establish a unicast forwarding viaone or more of the inter-rail links, and via one or more of thegateways.

In accordance with an embodiment, a decision to stop using inter-raillinks for unicast traffic between one or more pairs of nodes can bebased upon, for example, a decision tree or a similar method. At thestart, the HAPS can determine when physical connectivity status changesin any of the rails so that physical connectivity is added orre-established. The HAPS can additionally determine if the change inphysical connectivity has provided that any pair of nodes that arecurrently using inter-rail links for communication is now able tocommunicate on either rail without any IRL dependency. Then, for allsuch pairs of nodes that can now communicate on either rail, the HAPScan remove relevant unicast forwarding via the IRLs.

In accordance with an embodiment, while the above description refers toonly a singular HAPS, one or ordinary skill in the art would appreciatethat the respective HAPS in various rails can communicate with eachother in negotiating the enablement and disablement of unicastforwarding over the one or more inter-rail links.

FIG. 23 is a flowchart of a method for on-demand unicast forwarding in ahigh performance computing environment, in accordance with anembodiment.

At step 2310, the method can provide, at a computer comprising one ormore microprocessors, a plurality of switches, a plurality of hostchannel adapters, and a plurality of hosts.

At step 2320, the method can provide, at two rails, redundantconnectivity between the plurality of hosts, wherein each rail comprisesa set of the plurality of switches.

At step 2330, the method can detect a disruption i connectivity betweentwo hosts of the plurality of hosts.

At step 2340, the method can re-establish communication between the twohosts of the plurality of hosts via unicast packets on an inter-raillink, the inter-rail link being provided between the two rails.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample, and not limitation. The embodiments were chosen and describedin order to explain the principles of the invention and its practicalapplication. The embodiments illustrate systems and methods in which thepresent invention is utilized to improve the performance of the systemsand methods by providing new and/or improved features and/or providingbenefits such as reduced resource utilization, increased capacity,improved efficiency, and reduced latency.

In some embodiments, features of the present invention are implemented,in whole or in part, in a computer including a processor, a storagemedium such as a memory and a network card for communicating with othercomputers. In some embodiments, features of the invention areimplemented in a distributed computing environment in which one or moreclusters of computers is connected by a network such as a Local AreaNetwork (LAN), switch fabric network (e.g. InfiniBand), or Wide AreaNetwork (WAN). The distributed computing environment can have allcomputers at a single location or have clusters of computers atdifferent remote geographic locations connected by a WAN.

In some embodiments, features of the present invention are implemented,in whole or in part, in the cloud as part of, or as a service of, acloud computing system based on shared, elastic resources delivered tousers in a self-service, metered manner using Web technologies. Thereare five characteristics of the cloud (as defined by the NationalInstitute of Standards and Technology: on-demand self-service; broadnetwork access; resource pooling; rapid elasticity; and measuredservice. Cloud deployment models include: Public, Private, and Hybrid.Cloud service models include Software as a Service (SaaS), Platform as aService (PaaS), Database as a Service (DBaaS), and Infrastructure as aService (IaaS). As used herein, the cloud is the combination ofhardware, software, network, and web technologies which delivers sharedelastic resources to users in a self-service, metered manner. Unlessotherwise specified the cloud, as used herein, encompasses public cloud,private cloud, and hybrid cloud embodiments, and all cloud deploymentmodels including, but not limited to, cloud SaaS, cloud DBaaS, cloudPaaS, and cloud IaaS.

In some embodiments, features of the present invention are implementedusing, or with the assistance of hardware, software, firmware, orcombinations thereof. In some embodiments, features of the presentinvention are implemented using a processor configured or programmed toexecute one or more functions of the present invention. The processor isin some embodiments a single or multi-chip processor, a digital signalprocessor (DSP), a system on a chip (SOC), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA) orother programmable logic device, state machine, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. In someimplementations, features of the present invention may be implemented bycircuitry that is specific to a given function. In otherimplementations, the features may implemented in a processor configuredto perform particular functions using instructions stored e.g. on acomputer readable storage media.

In some embodiments, features of the present invention are incorporatedin software and/or firmware for controlling the hardware of a processingand/or networking system, and for enabling a processor and/or network tointeract with other systems utilizing the features of the presentinvention. Such software or firmware may include, but is not limited to,application code, device drivers, operating systems, virtual machines,hypervisors, application programming interfaces, programming languages,and execution environments/containers. Appropriate software coding canreadily be prepared by skilled programmers based on the teachings of thepresent disclosure, as will be apparent to those skilled in the softwareart.

In some embodiments, the present invention includes a computer programproduct which is a storage medium or computer-readable medium (media)having instructions stored thereon/in, which instructions can be used toprogram or otherwise configure a system such as a computer to performany of the processes or functions of the present invention. The storagemedium or computer readable medium can include, but is not limited to,any type of disk including floppy disks, optical discs, DVD, CD-ROMs,microdrive, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs,DRAMs, VRAMs, flash memory devices, magnetic or optical cards,nanosystems (including molecular memory ICs), or any type of media ordevice suitable for storing instructions and/or data. In particularembodiments, the storage medium or computer readable medium is anon-transitory storage medium or non-transitory computer readablemedium.

The foregoing description is not intended to be exhaustive or to limitthe invention to the precise forms disclosed. Additionally, whereembodiments of the present invention have been described using aparticular series of transactions and steps, it should be apparent tothose skilled in the art that the scope of the present invention is notlimited to the described series of transactions and steps. Further,where embodiments of the present invention have been described using aparticular combination of hardware and software, it should be recognizedthat other combinations of hardware and software are also within thescope of the present invention. Further, while the various embodimentsdescribe particular combinations of features of the invention it shouldbe understood that different combinations of the features will beapparent to persons skilled in the relevant art as within the scope ofthe invention such that features of one embodiment may incorporated intoanother embodiment. Moreover, it will be apparent to persons skilled inthe relevant art that various additions, subtractions, deletions,variations, and other modifications and changes in form, detail,implementation and application can be made therein without departingfrom the spirit and scope of the invention. It is intended that thebroader spirit and scope of the invention be defined by the followingclaims and their equivalents.

What is claimed is:
 1. A system for on-demand unicast forwarding in ahigh performance computing environment, comprising: a computer, thecomputer comprising one or more microprocessors; and a plurality ofswitches; a plurality of host channel adapters; and a plurality ofhosts; wherein two rails are provided, the two rails providing redundantconnectivity between the plurality of hosts, wherein each rail comprisesa set of the plurality of switches; wherein connectivity between twohosts of the plurality of hosts is disrupted; wherein communicationbetween the two hosts of the plurality of hosts is re-established viaunicast packets on an inter-rail link, the inter-rail link beingprovided between the two rails.
 2. The system of claim 1, wherein thetwo hosts of the plurality of hosts belong to a same partition.
 3. Thesystem of claim 2, wherein a high availability path service is providedin each of the two rails.
 4. The system of claim 3, wherein each of thehigh availability path services are associated with a storage, andwherein the each high availability path service records in therespective storage a record of all connectivity between each of theplurality of hosts
 5. The system of claim 4, wherein the re-establishingof communication is performed by a negation between the highavailability path services of the two rails and is based at least uponthe record of all connectivity between each of the plurality of hosts.6. The system of claim 3, wherein a high availability path servicedetects that the connectivity between the two hosts is restored.
 7. Thesystem of claim 6, wherein upon such detection of a restoredconnectivity, communication between the two hosts via the inter-raillink is stopped.
 8. A method for on-demand unicast forwarding in a highperformance computing, comprising: providing, at a computer, thecomputer comprising one or more microprocessors, a plurality ofswitches; a plurality of host channel adapters; and a plurality ofhosts; providing, at two rails, redundant connectivity between theplurality of hosts, wherein each rail comprises a set of the pluralityof switches; detecting a disruption i connectivity between two hosts ofthe plurality of hosts; re-establishing communication between the twohosts of the plurality of hosts via unicast packets on an inter-raillink, the inter-rail link being provided between the two rails.
 9. Themethod of claim 8, wherein the two hosts of the plurality of hostsbelong to a same partition.
 10. The method of claim 9, wherein a highavailability path service is provided in each of the two rails.
 11. Themethod of claim 10, wherein each of the high availability path servicesare associated with a storage, and wherein the each high availabilitypath service records in the respective storage a record of allconnectivity between each of the plurality of hosts
 12. The method ofclaim 11, wherein the re-establishing of communication is performed by anegation between the high availability path services of the two railsand is based at least upon the record of all connectivity between eachof the plurality of hosts.
 13. The method of claim 10, wherein a highavailability path service detects that the connectivity between the twohosts is restored.
 14. The method of claim 13, wherein upon suchdetection of a restored connectivity, communication between the twohosts via the inter-rail link is stopped.
 15. A non-transitory computerreadable storage medium having instructions for on-demand unicastforwarding in a high performance computing, which when read and executedcause a computer to perform steps comprising: providing, at a computer,the computer comprising one or more microprocessors, a plurality ofswitches; a plurality of host channel adapters; and a plurality ofhosts; providing, at two rails, redundant connectivity between theplurality of hosts, wherein each rail comprises a set of the pluralityof switches; detecting a disruption i connectivity between two hosts ofthe plurality of hosts; re-establishing communication between the twohosts of the plurality of hosts via unicast packets on an inter-raillink, the inter-rail link being provided between the two rails.
 16. Thenon-transitory computer readable storage medium of claim 15, wherein thetwo hosts of the plurality of hosts belong to a same partition.
 17. Thenon-transitory computer readable storage medium of claim 16, wherein ahigh availability path service is provided in each of the two rails. 18.The non-transitory computer readable storage medium of claim 17, whereineach of the high availability path services are associated with astorage, and wherein the each high availability path service records inthe respective storage a record of all connectivity between each of theplurality of hosts
 19. The non-transitory computer readable storagemedium of claim 18, wherein the re-establishing of communication isperformed by a negation between the high availability path services ofthe two rails and is based at least upon the record of all connectivitybetween each of the plurality of hosts.
 20. The non-transitory computerreadable storage medium of claim 17, wherein a high availability pathservice detects that the connectivity between the two hosts is restored;and wherein upon such detection of a restored connectivity,communication between the two hosts via the inter-rail link is stopped.